Multiple access wireless communications system using a multisector configuration

ABSTRACT

Power control methods and apparatus for use in a sectorized cell of an OFDM communications system are described. Each sector of a cell uses the same frequencies and transmission times and is synchronized with the other sectors in the cell in terms of tone frequencies used at any given time and symbol transmission times. Tones are allocated to channels in each cell in the same manner so that each channel in a sector has a corresponding channel in another sector. Power differences between channels in different sectors are maintained to be within a pre-selected power difference. Different channels in a cell are assigned different power levels. Wireless terminals are assigned to channels based on channel feedback information. Wireless terminals with poor channel conditions are allocated to higher power channels than wireless terminals with good channel conditions. Lower power channels often include more tones per symbol time than high power channels.

RELATED APPLICATIONS

The present invention claims the benefit of U.S. Provisional Patent No.60/406,076 filed Aug. 26, 2002.

BACKGROUND OF THE INVENTION

Spread spectrum OFDM (orthogonal frequency division multiplexing)multiple access, is one example of a spectrally efficient wirelesscommunications technology. OFDM can be used to provide wirelesscommunication services.

In OFDM spread spectrum system, the total spectral bandwidth is normallydivided into a number of orthogonal tones, e.g. subcarrier frequencies.In a cellular network, the same bandwidth is often reused in all thecells of the system. Those tones hop across the bandwidth for thepurpose of channel (frequency) diversity and interference averaging.Tone hopping follows predefined tone hopping sequences so that thehopped tones of a given cell do not collide with each other. The tonehopping sequences used in neighboring cells could be different toaverage interference between cells.

One exemplary form of the tone hopping sequences, is

$\begin{matrix}{{F_{j}(t)} = {\frac{SLOPE}{\left\{ {{\frac{1}{j}{mod}\; N} + t} \right\}}\;{mod}\; N}} & (1)\end{matrix}$

In the above equation, N is the total number of the tones, t is the OFDMsymbol index, j is the index of a tone hopping sequence, j=0, . . . ,N-1, and F_(j)(t) is the index of the tone occupied by the j-th tonehopping sequence at time t. SLOPE is a cell specific parameter thatuniquely determines the tone hopping sequences used in a given cell.Neighboring cells could use different values of SLOPE.

Information (control and data) is transported via various physicalchannels. A physical channel corresponds to one or more tone hoppingsequences defined in Equation (1). Therefore, those tone hoppingsequences are sometimes referred to as data tone hopping sequences. In aphysical channel, the basic transmission unit is a channel segment. Achannel segment includes the tones corresponding to the data tonehopping sequence(s) of the data channel over some time interval usuallycorresponding to a number of OFDM symbols.

In addition to the data tone hopping sequences, the OFDM spread spectrumsystem may also use a pilot in a downlink to facilitate variousoperations, such operations may include synchronization and channelestimation. A pilot normally corresponds to one or more pilot tonehopping sequences. One exemplary form of a pilot tone hopping sequence,as disclosed in U.S. patent application Ser. No. 09/551,791, isPilot_(j)(t)=SLOPE·t+O _(j) mod N  (2)

By using different values for SLOPE, different pilot sequences willoccur. Different pilot sequences may be used in different cells.

In the above equation, N, t, and SLOPE are the same parameters as usedin Equation (1), j is the index of a pilot tone hopping sequence,Pilot_(j)(t) is the index of the tone occupied by the j-th pilot tonehopping sequence at time t, and O_(j) is a fixed offset number of thej-th pilot tone hopping sequence. Normally, the cells in a system usethe same set of offsets {O_(j)}.

In the OFDM spread spectrum system, the pilot and data tone hoppingsequences are normally periodic with the same periodicity and use thesame value for parameter SLOPE. The time interval of one period of atone hopping sequence is sometimes referred to as a super slot. Thus, asuper slot corresponds to a period after which a pilot sequence willrepeat. The structures of the pilot, physical channels, and channelsegments generally repeat from one super slot to another, and thereforecan be uniquely determined once the super slot boundaries have beenidentified.

FIG. 1 shows a frequency vs time graph 100 used to illustrate generalconcepts of data and pilot tone hopping sequences, control and datatraffic channels, channel segments, and super slots.

FIG. 1 includes a first row 102, a second row 104, a third row 106, afourth row 108, and a fifth row 110. Each row 102, 104, 106, 108, 110corresponds to a different orthogonal frequency tone in the frequencydomain.

FIG. 1 also includes a first column 112, a second column 114, a thirdcolumn 116, a fourth column 118, a fifth column 120 a sixth column 122,a seventh column 124, an eighth column 126, a ninth column 128, and atenth column 130. Each column 112, 114, 116, 118, 120, 122, 124, 126,128, 130 corresponds to an OFDM symbol time in the time domain.

In the FIG. 1 example, super slots 133, 135 each have a period equal tothe period of the tone hopping sequence. First super slot 133 has aperiod of five OFDM symbol times represented by first through fifthcolumns 112, 114, 116, 118, 120 and defined by vertical time domainboundary lines 111 and 121. Second super slot 135 also has a period offive OFDM symbol times. Super slot 135 corresponds to sixth throughtenth columns 122, 124, 126, 128, 130 and is defined by vertical timedomain boundary lines 121 and 131.

During the first super slot (columns 112, 114, 116, 118, 120), data tonehopping sequences are shown for a first traffic segment. Three tones arededicated to the first traffic segment during each symbol period. Thedata tone hopping sequence for the first exemplary traffic channelsegment is illustrated by diagonal line shading which descends in FIG. 1from left to right. During the second super slot (columns 122, 124, 126,128, 130), data tone hopping sequences are shown for a second trafficsegment. The data tone hopping sequence repeats in each super slot 133,135. The data tone hopping sequence for the second exemplary trafficchannel segment is illustrated by ascending diagonal line shading inFIG. 1. During the OFDM time intervals represented by first column 112and the sixth column 122, the traffic channel data is shown to includefrequency tones represented by first row 102, second row 104 and thirdrow 106. During the OFDM time intervals represented by second column 114and the seventh column 124, the traffic channel data is shown to includefrequency tones represented by first row 102, third row 106 and fifthrow 110. During the OFDM time intervals represented by third column 116and the eighth column 126, the traffic channel data is shown to includefrequency tones represented by second row 104, fourth row 108 and fifthrow 110. During the OFDM time intervals represented by fourth column 118and the ninth column 128, the traffic channel data is shown to includefrequency tones represented by first row 102, third row 106 and fourthrow 108. During the OFDM time intervals represented by fifth column 120and the tenth column 130, the traffic channel data is shown to includefrequency tones represented by second row 104, third row 106 and fourthrow 108.

FIG. 1 also shows a pilot tone hopping sequence. The pilot tone hoppingsequence repeats in each super slot 133, 135. The pilot tone hoppingsequence is illustrated in FIG. 1 by use of small horizontal lineshading. During the OFDM time intervals represented by first column 112and the sixth column 122, the pilot tone is assigned to the frequencytone represented by fifth row 110. During the OFDM time intervalsrepresented by second column 114 and the seventh column 124, the pilottone is assigned to the frequency tone represented by fourth row 108.During the OFDM time intervals represented by third column 116 and theeighth column 126, the pilot tone is assigned to the frequency tonerepresented by third row 106. During the OFDM time intervals representedby fourth column 118 and the ninth column 128, the pilot tone isassigned to the frequency tone represented by the second row 104. Duringthe OFDM time intervals represented by fifth column 120 and the tenthcolumn 130, the pilot tone is assigned to the frequency tone representedby the first row 102.

In some OFDM spread spectrum systems, the traffic channel is assigned ina segment-by-segment manner. Specifically, traffic channel segments canbe independently assigned to different wireless terminals. A schedulerdetermines the amount of transmission power and the burst data rate,associated with a particular channel coding and modulation scheme, to beused in each traffic channel segment. The transmission powers and burstdata rates of different traffic channel segments may be different.

Sectorization is a popular method to improve wireless system capacity.For example, FIG. 2 illustrates a cell 200 including three sectors:sector 1 201, sector 2 203, and sector 3 205. Cell 200 also includes abase station 207 employing a 3-sector antenna including antenna sector 1209, antenna sector 2 211, and antenna sector 3 213. The sectorizedantenna provides some isolation between the sectors 201, 203, 205. In anideal system, the same spectrum can be reused in all the sectors 201,203, 205 without interfering with each other, thereby tripling thesystem capacity (over an omni cell) in the 3-sector system shown in FIG.2. Unfortunately, ideal signal separation is not possible in the realworld, which generally complicates the use of sectorization in somesystems.

In theory, integrating the sectorization into an OFDM spread spectrumsystem should improve the overall system performance. Howeverinterference between the sectors due to the limited antenna isolationand reflection from objects can limit the actual capacity gains over anomni cell. Accordingly, it can be appreciated that there is a need formethods and apparatus which will allow sectorization to be used in OFDMsystems in a manner that will improve the capacity of such systemswithout many of the interference problems associated with sectorization.

SUMMARY OF THE INVENTION

In accordance with the invention, the same spectrum, e.g., frequencies,may be reused in each of a cell's sectors in a sectorized FDM system. Insome embodiments of the invention, the sectors of a cell aresynchronized in terms of tone frequencies, OFDM symbol timing, data tonehopping sequences, channel segments and super slot boundaries.Synchronization of fewer transmission characteristics or parameters isused in some embodiments. In fact, some features of the invention suchas beacon signals discussed below may be used with minimal or nofrequency synchronization between sectors of a cell.

In various embodiments symbol timing between sectors of a cell issubstantially synchronized, e.g., the symbol transmission start timesare synchronized to within the time duration of a cyclic prefix includedin transmitted symbols. As is know in the art, it is common to add acyclic prefix, e.g., a copy of a portion of the symbol so that the samedata is at both ends of the transmitted symbol. Cyclic prefixes providesome protection against timing errors and can be used as a buffer interms of amount of acceptable timing differences which may occur betweensectors.

Different cells in the system may, but need not, be synchronized inregard to transmission characteristics such as frequency. In thesynchronized sector embodiment, for any control or data traffic channelin a given sector, there is a corresponding control or data trafficchannel in each of the other synchronized sectors of the same cell. Thecorresponding channels in the different sectors will have the sameconfiguration of frequency tones and time intervals, e.g., transmissionfrequencies and symbol transmission times. Channels are divided intosegments for transmission purposes. Thus, corresponding channels willhave corresponding channel segments. Because of the high level ofsynchronization between the sectors in the fully synchronized sectorembodiment, inter-sector interference is concentrated betweencorresponding channel segments in such an embodiment. Non-correspondingchannel segments see comparatively little inter-sector interferencebetween each other.

In some embodiments, the pilots used in each of the sectors of a cellhave the same value of SLOPE, but different offsets. This results in therepeating sequence of pilot tones being the same in each sector, but thestarting point of the sequence being different in terms of time. Thus,at any point in time, the pilots in different sectors of a cell may bedifferent.

When the sectorized OFDM spread spectrum system is used in a cellularnetwork, in accordance with the invention, neighboring cells may usedifferent values of SLOPE to determine the pilot and channel tonehopping sequences. The slope offset sets may be the same in differentcells. Different cells need not, and are not necessarily synchronized,in terms of tone frequencies, OFDM symbol timing, tone hoppingsequences, channel segments or super slot boundaries.

In accordance with one feature of the invention, in some embodiments,the transmission power allocated to corresponding channel segments ofdifferent sectors of a cell, if active, are substantially the same ineach of the sectors. In such a case, the difference between thetransmission powers for the corresponding active channel segments in thesectors of a cell are no more than Delta, where Delta is a value used tocontrol channel power differences between sectors. Different Deltas maybe used for different channels. In one embodiment, for at least onechannel, Delta is set to be a constant, for example, zero. In anotherembodiment, Delta may be different from one group of correspondingchannels to another, from one group of corresponding channel segments toanother, or as a function of burst data rates used in correspondingchannel segments or some other criteria. A scheduler may be used tocoordinate the power allocation in the various sectors of a cell in acentralized manner. In accordance with the invention, the dynamic rangeof the allocated power between the traffic channels in the same sectormay be large, while the dynamic range of the allocated power acrosscorresponding traffic channels in the various sectors is limited. Insome embodiments, the difference between corresponding channels ofdifferent sectors is kept to under less than 3 dB relative powerdifference for channel segments which are actively used in each of acells sectors.

In order to facilitate differentiation of the signals corresponding tochannel segments of different sectors, distinct scrambling bit sequencesmay, and sometimes are, used in different sectors when generatingtransmit signals in the respective sectors. The wireless terminalreceiver may use a particular scrambling bit sequence to selectivelydemodulate the signal from an intended sector transmission of a basestation. Alternatively, the wireless terminal receiver may use multiplescrambling bit sequences to demodulate the signals from multiple sectortransmissions of a base station or from multiple base stationssimultaneously.

The channel condition of a wireless terminal may be described in termsof being in one of two characteristic regions. In the first region, theSIR is not limited by inter-sector interference. When in the firstregion, the base station can increase the received SIR by allocatinghigh transmission power and thereby provide an improved SIR. In thesecond region, the SIR is limited by the inter-sector interference, inwhich case, allocating high transmission power may not remarkablyincrease the received SIR since inter-sector interference will increaseas channel power is uniformly increased in the corresponding channel ofeach sector.

In some embodiments, the wireless terminal estimates its channelcondition characteristics and notifies the base station, such that thebase station can make sensible scheduling decisions in terms of powerand burst data rate allocation. The channel condition information mayinclude information distinguishing between inter-sector interference andother interference. In accordance with the invention, the base station'sscheduler may use the reported channel condition characteristics of thewireless terminals including power information, signal strength, and SIRto match wireless terminals to appropriate channels in each sector.Decisions on providing additional power or allocating segments for awireless terminal to a channel having high power can be made based onthe indication of inter-sector interference relative to otherinterference. In this manner, wireless terminals which can benefit fromhigher transmission power, e.g., those subject to low inter-sectorinterference, can be allocated to high power channels in a preferentialmanner over wireless terminals subject to comparatively highinter-sector interference. Assignment of high power channel segments canbe used to load balance the system, improve or optimize systemperformance and/or increase throughput capability by evaluating andreducing inter-sector and inter-cell interference.

In accordance with one embodiment of the invention, if a wirelessterminal is operating within a sector's cell boundary region andassigned a channel segment, the cell's scheduler may leave the tonescorresponding to the channel segment in the sector adjacent the boundaryregion unassigned to reduce or eliminate the inter-sector interference.In accordance with the invention, sectorization isolation betweenwireless terminals in non-sector boundary areas may be managed by thescheduler's selective assignment of channel segments corresponding tochannels with different power levels to different wireless terminals.Low power channels segments are normally assigned to wireless terminalsnear the transmitter while high power channels segments are assigned towireless terminals far from the base station. The number of low powerchannels in a sector normally exceeds the number of high power channelswith, in many cases, more of the sector's total transmission power beingallocated to the relatively few high power channels than the largenumber of low power channels.

The base station may frequently and/or periodically transmit a beaconsignal, e.g., a relatively high power signal on one or a few tones, overa period of time, e.g., one symbol period. Transmission power isconcentrated on one or a small number of tones, e.g., the tones of thebeacon signal, during the beacon transmission. This high concentrationof power may involve allocating 80% or more of a sector's totaltransmission power in the beacon tones. In one embodiment, the beaconsignal is transmitted at a fixed OFDM symbol duration, for example, thefirst or the last OFDM symbol, of a super slot and may repeat everysuper slot or every few super slots. In such a case, beacon signals areused to indicate superslot boundaries. Therefore, once the time positionof the beacon signal has been located, the super slot boundaries can bedetermined. In accordance with the invention, beacon signals may beassigned to perform different tasks, e.g., convey different types ofinformation. Beacons may be assigned to use fixed predefinedfrequencies, the frequency itself may convey information, such as, e.g.,boundaries of a frequency band or the frequency may correspond to anindex number, such as e.g., sector index number. Other beacons may beassigned multiple or varying frequencies which may be related to anindex number or numbers used to convey information, such as, a slopevalue used to determine the hopping sequence of the cell into which thebeacon is transmitted. The set of tones that carry high power in thebeacon signal may be selected from a predefined group of beacon tonesets depending on the information to be conveyed. Use of differentbeacon tone sets in the beacon signal can indicate certain systeminformation, such as the values of SLOPE, boundaries of the frequencyband, and sector index.

In one embodiment of the invention, the type of beacon transmittedvaries as a function of transmission time, e.g., alternates in the timedomain. In another embodiment of the invention, the beacon frequencytone assignments may be reconfigured if a failure or problem occurs at aspecific tone frequency. By utilizing both the time and frequency domainto vary the beacon signal transmissions and the information conveyed, alarge amount of information may be conveyed to the mobiles in anefficient manner. This information may be used, e.g., to determine thesector/cell location of the mobile, offload some of the functionsrequired by the pilot such as e.g. synchronization to superslotboundaries, reduce the time required for pilot punch through, evaluatereception strength, and provide useful information to predict andimprove the efficiency of hand-offs between sectors and cells.

In accordance with the invention, in some embodiments, the frequency,symbol timing, and super slot structures of an uplink signal are slavedto those of the downlink signal, and are synchronized in the varioussectors of a cell. In one embodiment, the data tone hopping sequencesand channel segments are synchronized across each of the sectors of acell. In another embodiment, the data tone hopping sequences and channelsegments are randomized across each of the sectors of a cell such that achannel segment in one sector may interfere with multiple channelsegments in another sector of the same cell.

One embodiment of the beacon features of the invention is directed to amethod of operating a base station transmitter in a frequency divisionmultiplexed communications system. The base station transmitter uses aset of N tones to communicate information over a first period of timeusing first signals, said first period of time being at least twoseconds long, where N is larger than 10, and where the method includestransmitting during a second period of time a second signal including aset of X tones, where X is less than 5, and where at least 80% of amaximum average total base station transmission power used by said basestation transmitter during any 1 second period during said first periodof time is allocated to said set of X tones. The first period of timemay be a large time interval, e.g., several minutes, hours or days. Insome cases the first period of time is at least 30 minutes long. Inparticular implementations X is equal to one or two. The second periodof time may be a period of time, e.g., a symbol transmission period inwhich a beacon signal is transmitted. In some cases during the secondperiod of time at least half of the N-X tones which are in said set of Ntones but not in said set of X tones go unused during said second periodof time. In some implementations none of the N-X tones in said set of Ntones but not in said set of X tones are used during said second periodof time. In other implementations multiple ones of the N-X tones in saidset of N tones but not in said set of X tones are used during saidsecond period of time. The base station may be part of a communicationssystem which is an orthogonal frequency division multiplexed system. Insome OFDM implementations the second period of time is a period of timeused to transmit an orthogonal frequency division multiplexed symbol.The second period of time, e.g., the beacon transmission period, mayperiodically repeat during said first period of time. The method in thisexample may also include transmitting during a third period of time athird signal including a set of Y tones, where Y<N, each tone in saidthird set of Y tones having 20% or less of said maximum average totalbase station transmission power used by said base station transmitterduring any 1 second period during said first period of time, said thirdperiod of time having the same duration as said second period of time.The third period of time may be, and in some embodiments is, a symboltime in which data signals, pilot signals and/or control signals aretransmitted. The third period of time may be different from the secondperiod of time or overlap the second period of time. When the thirdperiod of time overlaps or is the same as the second period of time, asmall portion of the total power transmitted during the period of timeis available for use by the data, pilot and/or control signals which aremodulated on the Y tones, e.g., 20% or less due to the consumption of atleast 80% power by the beacon signal(s), e.g., high power tone or tones.The high power tones, e.g., one or more beacon tones, may be and invarious embodiments are, transmitted at a predetermined fixed frequency.The predetermined frequency may, and often does, have a fixed frequencyoffset >0 from the lowest frequency tone in said set of N tones. Thisallows the beacon signal to provide an indication of the boundary of theset of N tones.

In various embodiments at least one of said X tones, e.g., beacon tones,is transmitted at a frequency which is determined as a function of atleast one of a base station identifier and a sector identifier. In manyimplementations, for each repetition of said second period of time insaid first period of time there are at least Z repetitions of said thirdperiod of time in said first period of time where Z is at least 10,e.g., there are many more data transmission symbol time periods thanbeacon signal symbol time periods. In some cases Z is at least 400,e.g., there are at least 400 data transmission symbol times for eachbeacon transmission signal time. In some implementations during a fourthperiod of time a fourth signal including G tones is transmitted, where Gis less than 5, and where at least 80% of said maximum average totalbase station transmitter power used by said base station transmitterduring any 1 second period during said first period of time is allocatedto said G tones. The G tones may correspond, e.g., to a symboltransmission time in which a different beacon signal from the onetransmitted in the second period of time is transmitted. In oneembodiment the frequency of at least one of said G tones is a functionof at least one of a base station identifier and a sector identifier,and said at least one of said G tones is not one of said set of X tones.In various implementations the second and fourth periods of timeperiodically repeat during said first period of time. In someembodiments, a base station includes a transmitter control routine whichincludes modules, e.g., software modules or blocks of code, whichcontrol the generation and transmission of the signals during each ofthe first, second, third and fourth transmission periods. A separatecontrol module may not be used for the first signal period when it isfully comprised of second, third and fourth signal transmission periodswith the control modules for these periods control transmission.Accordingly, transmission control means may include one or more softwaremodules with each software module controlling a different transmissionfeature, e.g., a separate transmission feature of the invention recitedin one of the pending claims. Thus, while a single transmitter controlroutine may be present in a base station, the single routine may, andoften does, include multiple different control modules.

A communication method for use in a base station of a sectorized cellwhich is directed to various synchronization features of the inventionwill now be described. In accordance with the method the base stationtransmits symbols, e.g., modulated symbols, into multiple sectors ofsaid cell using orthogonal frequency division multiplexed symbols. Thefrequency division multiplexed symbols are generated by modulatinginformation on one or more symbols and, in most cases, adding a cyclicprefix to the form the modulated symbol to be transmitted. The methodcomprises, in one embodiment, operating each sector to use a set oftones to transmit orthogonal frequency division multiplexed symbols,each orthogonal frequency division multiplexed symbol. The symbols aretransmitted at symbol transmission start times. Thus, each transmittedsymbol has a symbol transmission start time. In accordance with theinvention each sector is controlled to use the same set of tones, thesame duration of each symbol transmission period, and substantially thesame symbol start times. In various embodiments each of said orthogonalfrequency division multiplexed symbols include a cyclic prefix having acyclic prefix length. In some of these embodiments substantially thesame symbol transmission start times are such that the differencebetween the symbol transmission start times of any two adjacent sectorsare at most the amount of time used to transmit a cyclic prefix. A setof hopping sequences is often used to allocate tones to a first set ofcommunication channels in a first sector of said cell. The same set ofhopping sequences is used to allocate tones to a corresponding set ofcommunication channels in each of the other sectors of the cell. Eachhopping sequence has a start time. The start time of each hoppingsequence in said set of hopping sequences is the same in each of saidsectors in one embodiment. In order to allow devices to distinguishbetween signals corresponding to different sectors of a cell withdifferent information to be transmitted, e.g., modulated symbols, may besubject to a scrambling operation prior to transmission. Differentscrambling sequences are used in different sectors. Thus, the scramblingsequence provides a way of distinguishing between data corresponding todifferent sectors. Thus, in at least one embodiment, scrambling ofmodulation symbols is performed prior to transmitting said modulationsymbols using said transmitted symbols with a different scramblingsequence being used in each sector of the cell. The communicationchannels in each of the sectors of a cell are normally partitioned intosegments, segments of corresponding channels in each of the sectors ofthe cell have the same segment partitions and have segment start timeswhich are substantially the same, such that for a segment of a channelin one sector there is another segment of the corresponding channelwhere the two segments use the same set of hopping sequences and thesame segment start times. In some embodiments the segment start timesfor segments of the same channel in different cells differ by no morethan the time used to transmit a cyclic prefix. Pilot tones are oftentransmitted in each sector of the cell. In various embodiments themethod of the invention includes transmitting a portion of pilot tonesin each sector of the cell according to a pilot tone hopping sequence,the same pilot tone hopping sequence being used in each sector but witha different fixed tone offset being used in each of the sectors of acell. The pilot tone hopping sequence may be a slope hopping sequence.In such implementations, adjacent cells can use different slope valuesfor determining the slope hopping sequences to be used. In someimplementations, pilot tones in each sector of the cell are transmittedaccording to a set of pilot tone hopping sequences, the same set ofpilot tone hopping sequences being used in each sector but withdifferent fixed tone offsets being used in each of the sectors of thecell. In such a case, pilot tone hopping sequences in a set of pilottone hopping sequences corresponding to a sector are often offset fromeach other by a corresponding preselected set of offsets, thecorresponding preselected set of offsets being the same in each sectorof the cell. Furthermore in such a case the set of pilot tone hoppingsequences used in any two adjacent sectors of the cell may not beidentical due to the use of different fixed tone offsets in the adjacentsectors. The set of pilot tone hopping sequences being used in any twoadjacent sectors of the cell need not be, and sometimes are notidentical, due to the use of different fixed tone offsets in theadjacent sectors for the pilot tone hopping sequences.

The power control methods of the present invention can be used alone orin combination with the other features and/or methods of the invention.In accordance with an exemplary power control method of the invention, aset of tones is used in a cell. A transmitter in the cell transmits intoa first sector of said cell over a plurality of symbol times using tonesfrom said set of tones. The cell includes a second sector adjoining saidfirst sector. The transmitter transmits into said second sector on firstand second communications channels, the first communications channelincluding a first subset of said set of tones during each of a firstsubset of said plurality of symbol times, the second communicationschannel including a second subset of said set of tones during each ofsaid first subset of said plurality of times, said first subset of saidset of tones and said second subset of said set of tones being differentfrom each other during each symbol time. In one such implementation, theexemplary method includes operating the transmitter to transmit on saidfirst and second channels into said first sector in a synchronous mannerwith transmissions made by said transmitter into said second sector; andcontrolling a total transmission power of the tones corresponding to thefirst channel in the first sector during said first subset of saidplurality of symbol times to be greater than 20% and less than 500% of atotal power of the tones corresponding to the first channel transmittedinto the second sector, during said first subset of said plurality ofsymbol times. In some implementations controlling the total transmissionpower of the tones corresponding to the first channel includes limitingthe total power used in said first subset of symbol times to be no morethan a fixed fraction of a maximum average total transmission power usedby said transmitter in the first sector during any 1 hour period, saidfixed fraction also being used to limit the total transmission power ofthe tones corresponding to the first channel in the second sector duringthe first subset of symbol times to be no more than said fixed fractionof a maximum average total transmission power used by said transmitterin the second sector during any 1 hour period, said fixed fraction beingless than 100%. The symbol times are, in some implementations,orthogonal frequency division multiplexed symbol transmission timeperiods. In such cases the tones are normally orthogonal frequencydivision tones. The set of tones may be, and often is, different duringat least two symbol times. Symbols transmitted at different times maycorrespond to different symbol constellations. In some implementations,said transmitter transmits into said first sector symbols correspondingto a first constellation on said first channel during said first subsetof symbol times and transmits symbols corresponding to a secondconstellation during a second subset of said plurality of symbol times,the second constellation including more symbols than the firstconstellation, in such a case, the method includes controlling a totaltransmission power of the tones corresponding to the first channel inthe first sector during the second subset of said plurality of symboltimes to be greater than 50% and less than 200% of a total power of thetones transmitted in the second sector corresponding to the firstchannel during said second subset of said plurality of symbol times. Inanother embodiment the transmitter transmits into the first sectorsymbols at a first channel coding rate on said first channel during saidfirst subset of said plurality of symbol times and transmits symbols ata second channel coding rate during a second subset of said plurality ofsymbol times, said second channel coding rate being higher than saidfirst channel coding rate. In such an implementation, the method furthercomprises controlling a total transmission power of the tonescorresponding to the first channel in the first sector during the secondsubset of said plurality of symbol times to be greater than 50% and lessthan 200% of a total power of the tones transmitted in the second sectorcorresponding to the first channel during said second subset of saidplurality of symbol times. The total transmission power of thetransmitted tones corresponding to the first channel in the first sectorduring the first subset of said plurality of symbol times may be, and insome implementations is, equal to the total transmission power of thetransmitted tones in the first channel in the second sector during saidfirst subset of said plurality of symbol times. In many cases, the firstsubset of said plurality of symbol times will include many, e.g., atleast 14, consecutive symbol times. The method further comprisescontrolling the total power of the tones transmitted in the first sectorcorresponding to the first channel during a fourth subset of saidplurality of symbol times to be one of greater than 200% and less than50% of the total power of the tones transmitted in said first sectorcorresponding to the second channel during said fourth subset of saidplurality of symbol times. In some implementations the power controlmethod includes controlling the total power of the tones transmitted inthe first sector corresponding to the first channel during a fourthsubset of said plurality of symbol times to be one of greater than 200%and less than 50% of the total power of the tones transmitted in saidfirst sector corresponding to the second channel during said fourthsubset of said plurality of symbol times. The fourth subset of saidplurality of symbol times sometimes includes at least 14 consecutivesymbol times and in some cases more than 40. In some implementations thefirst and second sectors use a third communications channel during asecond subset of said plurality of symbol times, the thirdcommunications channel includes a third subset of said set of tonesduring each of said second subset of said plurality of symbol times. Insuch a case the power control method often further includes the step ofcontrolling the transmitter during said second subset of said pluralityof symbol times, to limit the total transmission power on tonescorresponding to said third communications channel transmitted by saidtransmitter to be less than 10% of the total transmission power used bysaid transmitter to transmit tones into said second sector correspondingto the third channel during said second subset of said plurality ofsymbol times. In some cases, to limit interference e.g., between sectorsfor segments used to transmit control signals, the method includescontrolling the transmitter during said second subset of said pluralityof symbol times, to limit total transmission power on tonescorresponding to said third communications channel transmitted by saidtransmitter to be zero. In various implementations, the method of theinvention is further directed to controlling the allocation ofresources, e.g., segments, corresponding to the third communicationschannel to wireless terminals. In such an implementation the methodincludes operating the base station or an apparatus included therein toidentify wireless terminals in a boundary area which corresponds to aboundary between said first and second sectors; and to allocate theresources, e.g., channel segments, corresponding to the said thirdchannel to at least one of said identified wireless terminals.Identifying wireless terminals in the boundary region may includereceiving from a wireless terminal first information indicating anamount of intersector interference measured by said wireless terminaland second information indicating an amount of background interferencemeasured by said wireless terminal. Identifying wireless terminals inboundary regions may alternatively or in addition, include receiving asignal, e.g., a location signal, from a wireless terminal in saidboundary area a signal indicating that said wireless terminal is in saidboundary area. In some power control embodiments, the first and secondsectors use said third communications channel during a third subset ofsaid plurality of symbol times, said third subset of said plurality ofsymbol times being different from said second subset of said pluralityof symbol times. In such a case, the method may further comprisecontrolling said transmitter during said third subset of said pluralityof symbol times, to use a total transmission power on tonescorresponding to said third communications channel transmitted by saidtransmitter into the first sector to be at least 1000% used by saidsecond sector to transmit tones corresponding to the third channel intothe second sector during said third subset of said plurality of symboltimes. This 1000% represents power 10 times that used in the secondsector. This power difference will often be sufficient to makeintersector interference seen in the first sector to be a relativelysmall component of signal interference. In some implementations saidfirst and second sector use said third communications channel during athird subset of said plurality of symbol times, said third subset ofsaid plurality of symbol times being different from said second subsetof said plurality of symbol times. In one such implementation the methodfurther includes: controlling said transmitter during said third subsetof said plurality of symbol times, to use a total transmission power ontones corresponding to said third communications channel transmitted bysaid transmitter into the first sector to be at least 1000% used by saidsecond sector to transmit tones corresponding to the third channel intothe second sector during said third subset of said plurality of symboltimes. In the power control implementations just discussed, a basestation control routine may include different segments of code toperform each of the recited control operations. Furthermore, whileantennas or other elements of the base station transmitter may bedifferent in each sector, in many implementations the common controllogic and control functionality associated with the base station isresponsible for controlling transmission in various sectors inaccordance with one or more features of the invention.

Additional features, benefits and embodiments of the present inventionare discussed in the detailed description which follows.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates the general concepts of data and pilot tone hoppingsequences, control and data traffic channels, channel segments, andsuper slots.

FIG. 2 shows a three sector cell with a base station employing a 3sector antenna.

FIG. 3 shows a three sector cell with a base station illustrating theconcept of inter-sector boundary interference regions.

FIG. 4 illustrates an exemplary communications system utilizing cellsectorization in accordance with the present invention.

FIG. 5 illustrates an exemplary access node that may be used in thecommunication system of FIG. 4 in accordance with the present invention.

FIG. 6 illustrates an exemplary end node that may be used in thecommunications system of FIG. 4 in accordance with the presentinvention.

FIG. 7 illustrates frequency tone synchronization throughout the sectorsof a cell in accordance with the present invention.

FIG. 8 illustrates OFDM symbol time synchronization throughout thesectors of a cell in accordance with the present invention.

FIG. 9 illustrates that in all the sectors of a cell, the tonefrequencies occupied by the j-th tone hopping sequence at any OFDM timeare identical and that the super slot boundaries are identical inaccordance with the present invention. FIG. 9 further illustrates theconcept of corresponding control or data channel segments within thesectors of a cell in accordance with the present invention.

FIG. 10 shows an exemplary case where the frequency tones aredistributed amongst two traffic channels. For each control or datatraffic channel, the tone hopping sequence at any OFDM time is identicalacross the three exemplary sectors of the cell in accordance with thepresent invention.

FIG. 11 illustrates exemplary pilot tone hopping sequences with the sameslope value but a different offset value in each sector of a cell inaccordance with the present invention.

FIG. 12 illustrates the concept of the pilot tone hopping sequence ofFIG. 11 puncturing the data sequence of FIG. 10 in accordance with thepresent invention.

FIG. 13 shows a table illustrating exemplary power allocation betweendifferent traffic channel segments in the same sector of a cell andacross the corresponding traffic channel segments in all the sectors ofa cell in accordance with one embodiment of the present invention.

FIG. 14 shows a graph of per tone power vs frequency tone for ordinaryOFDM signal.

FIG. 15 shows a graph of per tone power vs frequency tone for the timeof beacon signal transmission where the total power is concentrated onjust two tones in accordance with one implementation of the presentinvention.

FIG. 16 shows a graph of per tone power vs frequency tone for the timeof beacon signal transmission where the total power is concentrated onjust one tone in accordance with one implementation of the presentinvention.

FIG. 17 shows a graph of per tone power vs frequency tone for the timeof beacon signal transmission illustrating a predefined group of beacontone sets in accordance with one embodiment of the present invention.

FIG. 18 shows a graph of frequency vs OFDM symbol time illustrating theconcept of different functionality for successive beacons in the timedomain in accordance with one embodiment of the present invention.

FIG. 19 shows a graph of frequency vs OFDM symbol time illustrating theconcept of transmitting alternating beacons types in the time domain inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

With the OFDM spread spectrum system, the tones used in a given cell areall orthogonal. Therefore, the data hopping sequences and the physicalchannels do not interfere with each other. Given the wireless channelpropagation characteristics, depending on its location, a wirelessterminal may experience a large dynamic range of channel conditionsmeasured in terms of signal-to-interference ratio (SIR) orsignal-to-noise ratio (SNR). Such a property can be exploited to enhancethe system capacity. For example, in accordance with the invention, ascheduler may optimally balance the power allocation in the trafficchannel by serving simultaneously wireless terminals with dramaticallydifferent wireless channel conditions. In that case, a wireless terminalwith a bad wireless channel condition may be allocated with a largeportion of transmission power and possibly a small portion of bandwidththereby gaining service robustness, while another wireless terminal witha good wireless channel condition may be allocated with a small portionof transmission power and possibly a large portion of bandwidth and canstill achieve a high burst data rate.

The OFDM spread spectrum system of the invention can be combined withthe sectorized antenna to improve the overall system performance.However, in reality, antenna isolation is never perfect. A signaltransmitted in one sector may leak to another sector with an attenuationfactor, thereby causing interference between sectors, i.e., inter-sectorinterference. The inter-sector interference may reduce the gains ofpower and burst data rate allocation. For example, in the absence of theinter-sector interference, a wireless terminal with a good wirelesschannel condition may be allocated with a small portion of transmissionpower and can still achieve high burst data rate. In the presence of theinter-sector interference, the wireless terminal may not achieve thesame high burst data rate with the same amount of transmission power.The situation becomes especially severe when the inter-sectorinterference comes from a traffic channel that is transmitted at muchhigher power, for example to serve another wireless terminal with badchannel condition.

FIG. 3 illustrates an exemplary cell 300 including 3 sectors: sector 1301, sector 2 303, and sector 3 305 and a base station 307 including a 3sector antenna. The base station 307 may communicate with end nodes,e.g. mobile nodes or mobile terminals, situated at arbitrary locationswithin the cell 300 via wireless links. From an interferenceperspective, cells may be deemed to be comprised of sector boundaryareas where interference from a neighboring sector may be a severeproblem and non-sector boundary areas. In the FIG. 3 illustration of thecell 300, the non-sector boundary areas are distinguished from theboundary areas. The cell 300 includes non-sector boundary area 1 309,non-sector boundary area 2 311, and non-sector boundary area 3 313. Thecell 300 also includes sector boundary areas: sector 1-2 boundary area315, sector 2-3 boundary area 317, and sector 3-1 boundary area 319. Thelevel of sectorization isolation can be described in terms of the amountof leakage between the non-sector boundary areas 309, 311, and 313. Forexample if a mobile node is situated in non-sector boundary area 1 309leakage may occur from signal intended for sector 2 303 and signalintended for sector 3 305. The leakage in the non-sector boundary areas309, 311, 313, is typically −13 dB to −15 dB, and will depend on factorssuch as the base station 307 antenna type. In the sector boundaryregions (sometimes referred to as 0 dB regions), areas 315, 317, and 319the signal strength at the reception point, may be almost equivalentfrom the two adjacent sector antennas. The present invention describesmethod and apparatus to improve the capacity of the system when deployedin a sectorized configuration.

For the purpose of illustration and description, a 3-sector cell 300 isused in FIG. 3 and in the subsequent examples of FIGS. 7, 8, 9, 10, 11,12, and 13. However, it is to be understood that the present inventionis applicable to other sectorization scenarios. In a sectorized cell,the sectors are indexed. For example, in the 3-sector cell 300 of FIG.3, the sector indices can be 1, 2, and 3.

FIG. 4 illustrates an exemplary communications system 400 employing cellsectorization and wireless communication in accordance with the presentinvention. The communications system 400 includes a plurality of cells,cell 1 438, cell N 440. Cell 1 438 represents the coverage area foraccess node (AN) 1 402 located within cell 1 438. The access node 1 402may be, for example, a base station. Cell 1 438 is subdivided into aplurality of sectors, sector 1 442, sector Y 444. A dashed line 446represents the boundaries between sectors 442, 444. Each sector 442, 444represents the intended coverage area corresponding to one sector of thesectorized antenna located at the access node 1 402. Sector 1 442includes a plurality of end nodes (ENs), EN(1) 422, EN(X) 424 coupled toAN 1 402 via wireless links 423, 425, respectivley. Similarly, sector Y444 includes a plurality of end nodes, EN(1′) 426, EN(X′) 428 coupled toAN 1 402 via wireless links 427, 429, respectively. The ENs 422, 424,426, 428 may be, e.g., mobile nodes or mobile terminals and may movethroughout the system 400.

Cell N 440 is subdivided into a plurality of sectors, sector 1 448,sector Y 450 with sector boundaries 446′. Cell N 440 is similar to cell1 438 and includes an access node M 402′, and a plurality of ENs 422′,424′, 426′, 428′ coupled to AN M 402′ via wireless links 423′, 425′,427′, 429′, respectively.

The access nodes 402, 402′ are coupled to a network node 406 via networklinks 412, 414, respectively. The network node 406 is coupled to othernetworks nodes, e.g. other access nodes, intermediate node, Home AgentNodes or Authentication, Authorization Accounting (AAA) server nodes,via network link 420. The network links 412, 414, 420, may be, forexample, fiber optic cables.

FIG. 5 illustrates an exemplary access node 500 of the present inventionthat may be used in the communications system 400 of FIG. 4, e.g., AN1402 of FIG. 4. The access node 400 includes a processor 502, e.g., CPU,a wireless communications interface 504, a network/Internetworkinterface 506, and a memory 508. The processor 502, wirelesscommunications interface 504, network/Internetwork interface 506, andmemory 508 are coupled together by a bus 510 over which the elements502, 504, 506, 508, can exchange data and information.

The processor 502 controls the operation of the access node 500 byexecuting routines and utilizing data within the memory 528 in order tooperate the interfaces 504, 506, perform the necessary processing tocontrol basic functionality of the access node 500 and to implement thefeatures and improvements employed in the sectorized system inaccordance with the present invention.

The wireless communications interface 504 includes a receiver circuit512 and a transmitter circuit 514 coupled to sectorized antennas 516,518, respectively. The receiver circuit 512 includes a Descramblercircuit 520 and the transmitter circuit 514 includes a scrambler circuit522. The sectorized antenna 516 receives signals from one or more mobilenodes, e.g. EN1 422 of FIG. 4. The receiver circuit 512 processes thereceived signals. The receiver circuit 512 uses its descrambler 520 toremove the scrambling sequence if scrambling was used duringtransmission by the mobile node. The transmitter circuitry 514 includesa scrambler 522 which may be used to randomize the transmitted signal inaccordance with the present invention. The access node 500 may transmitsignal to the mobile nodes, e.g. EN1 422 of FIG. 4, over its sectorizedantenna 518.

The network/internetwork interface 506 includes a receiver circuit 524and a transmitter circuit 526 which will allow the access node 500 to becoupled to other network nodes, e.g. other access nodes, AAA servers,Home Agent Nodes, etc. and interchange data and information with thosenodes via network links.

The memory includes routines 528 and data/information 530. The routinesinclude signal generation routines 532 and a scheduler 534. Thescheduler 534 includes various routines such as an inter-sectorinterference routine 536, an inter-cell interference routine 538, apower allocation routine 540, and a wireless terminal/traffic segmentmatching routine 542. The data/information 530 includes data/controlinformation 544, pilot information 546, beacon information 548, tonefrequency information 550, OFDM signal timing information 552, data tonehopping sequences 554, channel segments 556, super slot boundaryinformation 558, slope values 560, pilot values 562, delta 564, burstdata rates 566, MN channel condition information 568, power information570, and MN sector information 572. The tone frequency information 550includes sets of tones used for different signals: set of N tones usedfor OFDM signals, sets of X tones used for some beacon signals, sets ofY tones used for OFDM signals, and sets of G tones used for other beaconsignals, and repetition rate information associated with the varioussets of tones. Power information 570 includes wide and narrowinter-sector transmission power control range information, inter-channeltransmission power allocation range information, boundary transmissionpower range information, and power levels allocated for the channels ineach sector.

The signal generation routines 532 utilize the data/info 530, e.g.,super slot boundary information 558, tone frequency information 550,and/or OFDM symbol timing information 552, to perform signalsynchronization and generation operations. Signal generation routine 532also utilizes the data/info, e.g., the data tone hopping sequences 554,data/control info 544, pilot info 546, pilot values 562, and/or sectorinformation 572 to implement data/control hopping and pilot hoppingsequences. In addition signal generation routine 532 may utilizedata/info 530, e.g., beacon info 530, to generate beacon signals inaccordance with the present invention.

The inter-sector interference routine performs operations using themethods of the present invention and the data/info 530, such as, pilotinfo 546, MN channel condition information 568, and MN sectorinformation 572 to evaluate and reduce inter-sector interference withina given cell. The inter-cell interference routine 536 utilizes themethods of the present invention and data/info 530, e.g., reported MNchannel condition information 568, and slope values 560, to evaluate andreduce the effects of inter-cell interference. The power allocationroutine 540 uses the methods of the present invention and data info,e.g. power info 570 and delta 564, to control the power allocation tothe various traffic channels, e.g., to optimize performance. Thewireless terminal/traffic and segment matching routine 542 uses thedata/info 530, e.g. MN channel condition information 568, powerinformation 570, channel segments 556, and burst data rates 566 toassign wireless terminals as a function of their power needs to be in anappropriate channel segment in accordance with the invention.

Various specific functions and operations of the access node 500 will bediscussed in more detail below.

FIG. 6 illustrates an exemplary end node (EN) 600, e.g. a wirelessterminal such as mobile node (MN), mobile, mobile terminal, mobiledevice, fixed wireless device, etc., that may be used in the exemplarycommunications system 400 of FIG. 4 in accordance with the presentinvention. In this application, at various locations, references may bemade to the end node using various terminology and various exemplaryembodiments of the end node such as, e.g., wireless terminal, mobilenode, mobile, mobile terminal, fixed wireless device, etc.; it is to beunderstood that the apparatus and methods of the invention are alsoapplication to the other embodiments, variations and descriptions of theend node. The end node 600 includes a processor 602, e.g., CPU, awireless communications interface 604, and a memory 606. The processor602, wireless communications interface 604, and memory 606 are coupledtogether by a bus 608 over which the elements 602, 604, and 606, caninterchange data and information.

The processor 602 controls the operation of the end node 600 byexecuting routines and utilizing data within the memory 606 in order tooperate the wireless communications interface 604, perform the necessaryprocessing to control basic functionality of the end node 600 whileimplementing the features and improvements employed in the sectorizedsystem in accordance with the present invention.

The wireless communications interface 604 includes a receiver circuit610 and a transmitter circuit 612 coupled to antennas 614, 616,respectively. The receiver circuit 610 includes a Descrambler circuit618 and the transmitter circuit 612 includes a scrambler circuit 620.The antenna 614 receives broadcast signals, e.g., from an access node,e.g. AN1 402 of FIG. 4. The receiver circuit 610 processes the receivedsignal and may use its descrambler 618, e.g., decoder, to removescrambling if scrambling was used during transmission by the accessnode. The transmitter circuitry 612 includes a scrambler 620, e.g.,encoder, which may be used to randomize the transmitted signal inaccordance with the present invention. The end node 600 may transmit theencoded signal to the access node over its antenna 616.

The memory 606 includes routines 622 and data/information 624. Theroutines 622 include hopping sequence routines 626, a channel conditionmonitoring/reporting routine 628, and a beacon signal routine 630. Thedata/information 624 includes MN channel condition information 632,power information 634, tone frequency information 636, OFDM signaltiming information 638, data tone hopping sequences 640, channelassignment information 642, super slot boundary information 644, slopevalues 646, pilot values 648, slope indexes 650, beacon info 652, sectoridentification 654, and cell identification 656.

The hopping routines 626 include a data/control hopping sequence routine634 and a pilot hopping sequence routine 632 which performs operationsusing the methods of the present invention and the data/info 624, suchtone frequency info 636, OFDM signal timing information 638, data tonehopping sequences 640, channel assignment information 642, super slotboundary information 644, slope values 646, and/or pilot values 648 toprocess the received data, identify the cell 656 and sector 654 that themobile 600 is operating in and the corresponding access node 500 of FIG.5 that is communicating with the end node 600. The channel conditionmonitoring/reporting routine 628 performs operations using the methodsof the present invention and data info 624, e.g., MN channel conditioninfo 632, power info 634, and channel assignment 642 to evaluate thestatus and quality of the wireless link to the access node 500 andsubsequently report that data back to the access node 500 for use inscheduling. The beacon signal routine 630 performs operations relatingto beacon signals in accordance with the methods of the presentinvention. Beacon signal routine 630 uses the data/info 624, e.g. beaconinfo 652, power info 634, tone frequency info 636, super slot boundaries644, and/or slope indexes 650 to perform functions such as, e.g.,synchronization of super slot boundaries, determine boundaries offrequency band and sector index 654, determine slope value 646,determine cell location 656 and pilot values 648.

Various specific functions and operations of the end node 600 will bediscussed in more detail below.

Physical layer full synchronization across the sectors will now bedescribed.

In accordance with the invention, the same spectrum is reused in each ofthe sectors in a cell of the sectorized OFDM spread spectrum system.Moreover, in accordance with one particular exemplary embodiment of theinvention, each of the sectors of a cell are fully synchronized in termsof tone frequencies, OFDM symbol timing, data tone hopping sequences,channel segments and super slot boundaries. While such synchronizationis desirable, aspects of the invention may be used in systems wheresynchronization between sectors in a cell is not so complete as in thecase of the particular exemplary embodiment. Specifically, in each ofthe sectors of a cell the same set of tones is used with identical setsof tone frequencies being included in each set. The OFDM symbol timingsare also identical. FIG. 7 700 illustrates the sets of the tonefrequencies used in each of 3 sectors which form a cell. The horizontalaxis 707 of FIG. 7 corresponds to frequency. Each vertical arrowrepresents a frequency tone.

Rows 701, 703, 705 each correspond to a different sector of theexemplary cell. The same set of N tones is used in each sector, with thetones used in each sector being indexed 0 through N-1.

FIG. 8 800 illustrates OFDM symbol timing used in the 3 sectors. Thehorizontal axis 807 of FIG. 8 represents how time can be divided in eachsector according to symbol times, e.g., the time used to transmit anOFDM symbol. Each division on the horizontal axis 807 marks the start ofa new symbol time in each of the sectors of a cell. Row 1 (801)corresponds to symbol times in sector 1 while rows 2 and 3 (803,805)correspond to symbol times in sectors 2 and 3 of the same cell. Notethat symbol start times are synchronized in the three sectors of thecell. Each of the sectors of the cell derive the data tone hoppingsequences using the same OFDM symbol index and the same value of SLOPEin Equation (1). Therefore, in each of the sectors, the tone frequenciesoccupied by the j-th tone hopping sequence at any OFDM time areidentical and the super slot boundaries are also identical.

Furthermore, the physical layer channels and channel segments areconstructed in the same way in each of the sectors in the exemplarycell. FIG. 9 shows a frequency vs time graph 900 to illustrate thecontrol and data traffic channels and channel segments in the 3 sectorsof the exemplary cell shown in FIG. 3.

FIG. 9 illustrates the transmission of symbols in each of the 3 sectorsof the exemplary cell shown in FIG. 3 during a single superslot. In theFIG. 9 example, each horizontal division corresponds to a symboltransmission time where the exemplary superslot corresponds to 5 symboltimes.

In the FIG. 9 example, a super slot 943, the time interval of one periodof the data/control tone hopping sequence, is shown as the concatenationof five OFDM symbol times, represented by first through fifth columns932, 934, 936, 938, 940 and defined by vertical time domain boundarylines 931 and 941.

FIG. 9 includes a first group of first through fifth rows 902, 904, 906,908, and 910 which correspond to a first sector of the cell. Each row902, 904, 906, 908, 910 corresponds to a different orthogonal frequencytone in the frequency domain of sector 1.

A second group of first through fifth rows 912, 914, 916, 918, and 920corresponds to a second sector of the cell. Each row 912, 914, 916, 918,920 corresponds to a different orthogonal frequency tone in thefrequency domain of sector 2.

A third group of first through fifth rows 922, 924, 926, 928, and 930corresponds to a third sector of the cell. Each row 922, 924, 926, 928,930 corresponds to a different orthogonal frequency tone in thefrequency domain of sector 3.

The same frequency tone is represented by first row 902 for sector 1,the first row 912 for sector 2, and the first row 922 for sector 3.Similarly, frequency tone equivalency exists across the three sectorsfor the following sets: (second row 904, second row 914, second row924), (third row 906, third row 916, third row 926), (fourth row 908,fourth row 918, fourth row 928), (fifth row 910, fifth row 920, fifthrow 930).

FIG. 9 also includes first through fifth columns 932, 934, 936, 938, and940. Each column 932, 934, 936, 938, 940 corresponds to an OFDM symboltime in the time domain.

Shading is used in FIG. 9 to illustrate segments corresponding to anexemplary channel within the particular sector. For example, during theOFDM time interval represented by first column 932, a traffic channelfor sector 1 corresponds to and uses the 3 tone frequencies representedby first row 902, second row 904, and third row 906. In the FIG. 9example, the three sectors allocate tones to channels using the sameallocation scheme. Thus in sectors 2 and 3 the same tones are used forthe channel as in sector 1.

As the OFDM symbol time changes through the superslot 943, data/controltone hopping occurs and the tone frequencies used by the data/controlchannels change. It can be seen that for the data/control trafficchannel segment in a given sector, there is a corresponding data/controltraffic channel segment in each of the other 2 sectors, since eachsector in the exemplary embodiment has the same configuration offrequency tones and time intervals. The segments in the 3 sectors whichcorrespond to the same channel are sometimes referred to as“corresponding channel segments.”

FIG. 10 shows a frequency vs time graph 1000 to illustrate multiplecorresponding data/control traffic channel segments in the 3 sectors.

First through fifteenth rows 1002, 1004, 1006, 1008, 1010, 1012, 1014,1016, 1018, 1020, 1022, 1024, 1026, 1028, 1030 of FIG. 10 correspond tothe same frequency tones as rows 902, 904, 906, 908, 910, 912, 914, 916,918, 920, 922, 924, 926, 928, 930 of FIG. 9, respectively. First thoughfifth columns 1032, 1034, 1036, 1038, 1040 of FIG. 10 correspond to thesame OFDM symbol times of first through fifth column 932, 934, 936, 938,and 940 of FIG. 9, respectively. A super slot 1043 defined by boundarylines 1031 and 1041 of FIG. 10, corresponds to the super slot 943 ofFIG. 9.

The area with line shading descending from left to right is used toindicate a first set of corresponding data/control traffic segments,e.g., segments which correspond to the same channel. The area with lineshading ascending from left to right represents a second correspondingdata/control traffic segment in FIG. 10. For example, in the OFDM timeinterval represented by second column 1034, the first data/controltraffic segment in sector 1 uses frequency tones represented by firstrow 1002, third row 1006, and sixth row 1010, while the seconddata/control traffic segment in sector 1 uses frequency tonesrepresented by second row 1004 and fourth row 1008.

In the exemplary implementation, it can be seen that for any control ordata traffic channel segment in a given sector, there is a correspondingcontrol or data traffic channel segment in each of the other 2 sectors,which has the same configuration of frequency tones and time intervals.Those segments in the 3 sectors are referred to as “correspondingchannel segments” in the following discussion. Note that because of thefull synchronization between the sectors, inter-sector interference isconcentrated between corresponding channel segments. Other channelsegments normally see little or negligible inter-sector interferencebetween each other.

FIG. 11 shows a frequency vs time graph 1100 to illustrate pilot tonehopping sequences in the 3 sectors.

First through fifteenth rows 1102, 1104, 1106, 1108, 1110, 1112, 1114,1116, 1118, 1120, 1122, 1124, 1126, 1128, 1130 of FIG. 11 correspond tothe same frequency tones as rows 902, 904, 906, 908, 910, 912, 914, 916,918, 920, 922, 924, 926, 928, 930 of FIG. 9, respectively. First thoughfifth columns 1132, 1134, 1136, 1138, 1140 of FIG. 11 correspond to thesame OFDM symbol times of first through fifth column 932, 934, 936, 938,and 940 of FIG. 9, respectively. A super slot 1143 defined by boundarylines 1131 and 1141 of FIG. 11, corresponds to the super slot 943 ofFIG. 9.

The pilot tone hopping sequences are indicated by horizontal lineshading in FIG. 11. Not all the pilot tone hopping sequences used ineach individual sector of a cell are the same to facilitate, among otherthings, sector identification of a mobile node. Thus, in FIG. 11 thepilot tone hopping sequences are shown to be different in each sector ofthe three sector cell. FIG. 11 illustrates the pilots by horizontalshading in the 3 sectors in a cell where no pilots overlap.

In accordance with the invention, the pilots used in each of theexemplary cell's sectors have the same value of SLOPE, but differentsets of offsets {O_(j)}. These known offsets may be included in thepilot value information 562 stored in the base station and/or the mobilenode pilot value offset information 648. In the example, in the 3-sectorcell, sector 1 uses offsets {O_(j,1)}, sector 2 uses offsets {O_(j,2)},and sector 3 uses offsets {O_(j,3)}. The offset sets {O_(j,1)},{O_(j,2)}, and {O_(j,3)} are not identical resulting in differentfrequencies being used for pilots in different sectors at the same time.In one embodiment, the offset sets are completely non-overlapping, thatis, no two elements in the offset sets are identical. Hence, the pilotsin different sectors do not interfere with each other. In anotherembodiment, {O_(j,2)} and {O_(j,3)} are derived from {O_(j,1)}:O_(j,2)=O_(j,1)+D₂ mod N, and O_(j,3)=O_(j,1)+D₃ mod N, for all j, whereD₂ and D₃ are two non-zero constants determined by the sector indices.

In accordance with the invention, the pilot hopping sequences and datahopping sequences multiplex. That is, at a given OFDM symbol time, ifone pilot sequence occupies the same tone as another data sequence, thenthe tone is used by the pilot sequence to the exclusion of the data thatwould have been transmitted on the tone. Effectively, the data sequenceis punctured at that OFDM symbol time. The punctured, e.g., omitted,data may be recovered from the transmitted data using error correctioncodes and error correction techniques.

FIG. 12 shows a frequency vs time graph 1200, which is a combination oroverlay of FIGS. 10 and 11 and is used to illustrate the data/controlsequences of FIG. 10 being punctured by the pilot sequence of FIG. 11.Each row corresponds to one frequency with each horizontal sectioncorresponding to a different symbol transmission time.

First through fifteenth rows 1202, 1204, 1206, 1208, 1210, 1212, 1214,1216, 1218, 1220, 1222, 1224, 1226, 1228, 1230 of FIG. 12 correspond tothe same frequency tones as rows 902, 904, 908, 910, 916, 918, 920, 922,924, 926, 928, 930 of FIG. 9, respectively. First though fifth columns1232, 1234, 1236, 1238, 1240 of FIG. 12 correspond to the same OFDMsymbol times of first through fifth column 932, 934, 936, 938, and 940of FIG. 9, respectively. A super slot 1243 defined by boundary lines1231 and 1241 of FIG. 12, corresponds to the super slot 943 of FIG. 9.

Line shading descending from left to right is used to indicate segmentscorresponding to a first data or control channel. Line shading ascendingfrom left to right indictes segments corresponding to a second data orcontrol corresponding channel. Circles on top of the data/controlchannel segments represent pilot tones punching through the data/controlsequences to the exclusion of the data which would have been transmittedin the segment.

When the sectorized OFDM spread spectrum system is used in a cellularnetwork, in accordance with the invention, neighboring cells usedifferent values of SLOPE to determine the pilot and data tone hoppingsequences. In the exemplary system of the invention, the offset sets{O_(j,1)}, {O_(j,2)}, and {O_(j,3)} are the same in each of the system'snumerous cells. Different cells need not, and often are not,synchronized in terms of tone frequencies, OFDM symbol timing, tonehopping sequences, channel segments or super slot boundaries even thoughwithin an individual cell sectors may have such features/characteristicsin common.

Power allocation across sectors of a cell and within a sector inaccordance with various features of the invention will now be described.

The fact that inter-sector interference mainly occurs betweencorresponding channel segments imposes a constraint on the powerallocation across corresponding channel segments in the sectors of acell.

For the sake of description, first suppose that corresponding channelsegments are all active, i.e., being used to transmit signals. Inaccordance with a feature of the invention, the transmission powerallocated to corresponding channel segments are substantially the samein each sector of a cell. For example, in the 3-sector system, if all 3corresponding channel segments are active, then the difference betweenthe transmission powers for those channel segments in the 3 sectorsshall be no more than a parameter, Delta. The scheduler 534 of FIG. 5,in the exemplary embodiment, is responsible for coordinating the powerallocation in each of the cell's sectors in a centralized manner.

The value of Delta, which may be stored in the base station as Deltainformation 564, affects the potential impact due to the inter-sectorinterference. For example, for a large Delta, the transmission powers oftwo corresponding channel segments may be quite different. Consequently,the inter-sector interference may cause large interference on one of thetwo corresponding channel segments that has smaller transmission power.In one embodiment of the invention, Delta 564 is set to be a constant,for example, zero. In another embodiment of the invention, Delta 564 mayvary. Indeed, in accordance with the invention, the value of Delta 564may be different from one group of corresponding channel segments toanother. For example, Delta for corresponding control channel segmentsmay be, and sometimes is, different from that for corresponding datatraffic channel segments reflecting, from a policy perspective,tolerance for different levels of interference on different channels. Inone embodiment of the invention, Delta is a function of burst data ratesused in corresponding channel segments. For example, considercorresponding traffic channel segments. If one of the segments uses highchannel coding and modulation rate, for example to support high burstdata rate, a small value of Delta is desirable and, in accordance withthe invention, used. As part of its function, the scheduler 534determines the appropriate value of Delta 564 when the scheduler 534coordinates the power allocation and burst data rate allocation in thesectors of a cell.

In accordance with the invention, the scheduler 534, including routine542 of FIG. 5, can independently pick wireless terminals to be scheduledin corresponding data traffic channel segments of the cell's sectors.The achieved burst data rates depend on the power allocation determinedby routine 540 of FIG. 5 and the channel condition of the scheduledwireless terminals, e.g., as indicated by information 568, and thus maybe different in different sectors of a cell.

The constraint on the power allocation across corresponding channelsegments in the cell's sectors does not impose a similar constraint onthe power allocation across different channel segments within a sector.Indeed, in a given sector, different channel segments may be allocatedquite different amount of transmission power. For example, considercorresponding traffic channel segments. Suppose there are two trafficchannel segments at a given time. The scheduler 534 may assign viaroutine 542 of FIG. 5 a wireless terminal of bad channel condition tothe first traffic channel segment in each of the sectors, and assign awireless terminal of good channel condition to the second trafficchannel segment in each of the sectors. Then, the scheduler 534 canoptimally balance the power allocation in the two traffic channelsegments. For example, the scheduler 534 allocates via routine 540 alarge portion, e.g., 80% or more, of transmission power to the firsttraffic channel segments to gain service robustness for the bad channelwireless terminals, and a small portion, e.g., 20% or less, oftransmission power to the second traffic channel segments to achievehigh burst data rate. In accordance with the invention, the dynamicrange of the allocated power between the two traffic channel segments inthe same sector may be large, e.g., greater than 3 dB relative powerdifference while the dynamic range of the allocated power acrosscorresponding traffic channel segments in the cell's sectors is limited,e.g., less than 3 dB relative power difference in some embodiments.

FIG. 13 illustrates the power allocation between traffic channelsegments in the same sector and across corresponding traffic channelsegments in multiple sectors of a cell for an exemplary case with twotraffic channel segments, and a value of Delta=0. In Table 1300 of FIG.13, first column 1308 lists the traffic segment number, second column1310 lists the sector 1 power allocation information, third column 1312lists the sector 2 power allocation information, and fourth column 1314lists the sector 3 power allocation information. First row 1302 of table1300 lists column header information. Second row 1304 lists trafficchannel 1 power allocation information across the three sectors. Thirdrow 1306 lists traffic channel 2 power allocation information across thethree sectors. In the example, Delta=0, i.e., the allocation tocorresponding channels in each sector of the cell is the same while thedifference in allocation of power between channels is large, e.g., adifference being a factor of 4.

Consider the following exemplary embodiment of the invention including 2adjacent sectors, including 2 channels in each sector, and with basestation transmit power control on each channel within each sector of thecell in accordance with the invention.

CELL SECTOR 1 (S1) SECTOR 2 (S2) CHANNEL 1 (C1) CHANNEL 1 (C1) SECTOR 1POWER SECTOR 2 POWER CHANNEL 1 (S1PC1) CHANNEL 1 (S2PC1) CHANNEL 2 (C2)CHANNEL 2 (C2) SECTOR 1 POWER SECTOR 1 POWER CHANNEL 2 (S1PC2) CHANNEL 2(S1PC2)

The transmitter may be controlled to operate on a first and secondcommunications channel in a synchronous manner with transmissions madeinto both first and second sectors.

In the exemplary case, the total transmission power of the tonescorresponding to the first channel in the first sector of the cell(S1PC1) is controlled to be greater than 20% and less than 500% of thetotal power of the tones transmitted in the second sector correspondingto the first channel (S2PC1) during a period of time, e.g., a subset ofsymbol times. This may be represented by a first channel wideinter-sector transmission power control range: 20%<(S1PC1/S2PC1)<500%.

In some embodiments, controlling the total transmission power of thetones corresponding to the first channel includes limiting the totalpower used in the first subset of symbol times to no more than a fixedfraction of a maximum average total transmission power used by thetransmitter in the first sector during any 1 hour period, the fixedfraction also being used to limit the total transmission power of thetones corresponding to the first channel in the second sector during thefirst subset of symbol times to be no more than the fixed fraction of amaximum average total transmission power used by the transmitter in thesecond sector during any 1 hour period, said fixed fraction being lessthan 100%.

In some embodiments, the total transmission power of the tonescorresponding to the first channel in the first sector of the cell(S1PC1) is controlled to be greater than 50% and less than 200% of thetotal power of the tones transmitted in the second sector correspondingto the first channel (S2PC1) during a period of time, e.g., anothersubset of symbol times. This can be represented by a first channelnarrow inter-sector transmission power control range:50%<(S1PC1/S2PC1)<200%. The base station may monitor the number ofsymbols in a constellation being used for an interval of time, and usethat information to decide whether to apply the wide inter-sectorchannel control range or the narrow inter-sector channel control range.With a larger number of symbols in a constellation, e.g., modulationwith more elements per set, the channel is more susceptible tointerference noise, and therefore, the narrower inter-sector powercontrol range is selected by the base station, allowing the base stationto more tightly control the levels of interference between users withinsectors, and keep that interference level to an acceptably low level.The base may also make decisions as to whether to use the wideinter-sector power control range or the narrow inter-sector powercontrol range based upon the channel coding rate, e.g., is the codingrate a slower coding rate or a faster coding rate. If a channel is usingthe faster coding rate for an interval of time, the base station shoulduse the narrower inter-sector transmission power control range, sincethe faster range will make the user, more susceptible to interference,and interference levels between users can be more tightly controlled andmanaged by the base station to maintain an acceptable level if thenarrower inter-sector transmission power control range is used.

In some embodiments, the interval or period of time, e.g., the subsetsof symbol times at which the transmission power control on a particularchannel concerning two adjacent sectors uses a tighter inter-sectorpower control range or a narrower inter-sector power control range,includes at least 14 consecutive symbol times.

In some embodiments, the total transmission power of the tonescorresponding to the first channel in the first sector may be equal tothe total power of the transmitted tones in the first channel of thesecond sector during a period of time, e.g. interval of symbol times.This may be described as: S1PC1=S2PC1. FIG. 13 illustrates such a casewhere the power allocation to traffic segment 1=80% for both sector 1and sector 2 (second row 1304, column 2 1310 and columns 3 1312).

In some embodiments, within a given sector, e.g., the first sector, thetotal power of the tones transmitted in the first sector for the firstchannel (S1PC1) may be greater than 200% or less than 50% of the powerof the tones transmitted in the first sector for a second channel(S1PC2) for a period of time. This inter-channel transmission powercontrol range within a sector may be represented by: ((S1PC1/S1PC2)<50%)or (S1PC1/S1PC2>200%). In the example of FIG. 13 such an embodiment isshown, S1PC1=80% (second row 1304, second column 1310) and S1PC2=20%(third row 1306, second column 1310); S1PC1/S1PC2=400%. This allows awide range of power selections available to the base station to matchusers to power levels.

The interval of time at which the base station controls the differencein transmission power levels between the two channels within a givensector of a cell at greater than 200% or less than 50% may be a intervalof at least 14 consecutive symbol times.

In accordance with the invention, wireless terminals may be identifiedas being in boundary areas, e.g., sector boundary areas. The allocationof communication resources, e.g., channels, to wireless terminals may becontrolled. In accordance with the invention, those resources mayinclude a channel that limits the base station's total transmissionpower of its tones controlled to be <10% total transmission power of thecorresponding tones in the same channel in an adjacent sector to theboundary wireless terminal's sector. Thus, in such a case ratio of basestation total transmission power on corresponding tones for the samechannel between adjacent sectors would be 10% or less for one sector and1000% or more for the adjacent sector. In other embodiments, the <10%level may be 0%; effectively no power transmission on same channel inthe adjacent boundary sector. These implementation with a channel in onesector allocated little or no power, in accordance with the invention,is useful for operation of wireless terminals in sector boundary regionswhere high levels of interference would normally be experienced, e.g.regions 315, 317, and 319 of FIG. 3.

The identification and classification of wireless terminals 600 of FIG.6 to be in boundary areas, e.g., sector boundary regions, and theallocation or resources based upon the identification may be performedby the base station under the control routines 528 including theinter-sector interference routine 536 of FIG. 5, wirelessterminal/traffic & segment matching routine 542 of FIG. 5 and powerallocation routine 540. The identification of a wireless terminal 600 ina boundary area may be made based upon feedback information obtainedfrom the wireless terminal 600 that the base station 500 receives andprocesses; the feedback information may include experienced levels ofinter-sector interference, background interference and locationinterference. The wireless terminal 600 may collect MN channel conditioninfo 632 and report such information to the base station 500 under thedirection of the channel condition monitoring/reporting routine 628; theinformation will be available to the base station 500 in the MN channelcondition information 568.

Next, consider that corresponding channel segments need not all beactive. Note that an inactive segment does not cause inter-sectorinterference to other corresponding channel segments and is also notaffected by the inter-sector interference from other correspondingchannel segments. Therefore, in accordance with one embodiment of theinvention, when the scheduler 534 coordinates the power allocation in acell's sectors, only the active segments are taken into account.

If a wireless terminal, e.g., MN 600 of FIG. 6, is located at a sectorboundary, e.g., region 315, 317, or 319 of FIG. 3, it may experience asignificant amount of inter-sector interference. In one embodiment ofthe invention, the scheduler 534 uses inter-sector interference routine536 and matching routine 542, to assign segments of a first trafficchannel to a wireless terminal in a sector boundary and thecorresponding traffic channel segments to wireless terminals innon-sector boundary areas in the other sectors. In another embodiment ofthe invention, the scheduler 534 via routines 538 and 542 assigns onetraffic channel segment to a sector boundary wireless terminal, andkeeps one or more corresponding traffic channel segments inactive in theother sectors, so as to reduce the inter-sector interference. In such acase, frequencies assigned to the wireless terminal in the sectorboundary area will not be subjected to interference from adjacentsectors since the tones are left unused in those sectors. In oneembodiment, there is a pattern of utilizing a given traffic channelsegment, in which a sector periodically keeps the segment inactive whilesome of the other sectors keep the segment active. The pattern can befixed such that the sectors do not have to coordinate each other in areal time fashion. For example, one sector (sector A) keeps a trafficsegment inactive (i.e., not assign it to any wireless terminal in thesector), while the other two sectors (sectors B and C) assign thesegments to the wireless terminals in the sector boundaries between Aand B and between A and C. In the subsequent traffic segment, sector Bkeeps a traffic segment inactive while the other two sectors assign thesegments to the wireless terminals in the sector boundaries between Band A and between B and C. Then, in the subsequent traffic segment,sector C keeps a traffic segment inactive while the other two sectorsassign the segments to the wireless terminals in the sector boundariesbetween C and A and between C and B. The whole pattern then repeats,without explicit and real time coordination among the three sectors.

One consequence of full timing and frequency synchronization acrosssectors of a cell is that it may be difficult for a wireless terminal,e.g. MN 600 of FIG. 6, especially close to the sector boundary, e.g.,boundary 446 or 446′ of FIG. 4, to figure out which sector 654 of FIG.6, a received channel segment has come from. In order to differentiatethe channel segments across the sectors, distinct scrambling bitsequences may be used in different sectors.

Scrambling is a well-known method to randomize the transmitted signal.There are a number of ways to implement scrambling. Consider below aparticular implementation for illustration. It is understood that theprinciples of the invention do not rely on the particular exemplaryimplementation. At the transmitter 514 of FIG. 5, at a given OFDM symboltransmission time, symbols from various channel segments, generated bythe encoders of individual channel segments, are multiplexed to form asymbol vector, which is then used to generate the OFDM symbol signal tobe transmitted. The scrambling bit sequence is a random binary sequence,known to both the transmitter 514 and the receiver 610 of FIG. 6. Thesymbol vectors are phase-rotated in the exemplary embodiment based onthe scrambling bit sequence. At the receiver 610, the same scramblingbit sequence is used to de-rotate the received symbol before decodingtakes place.

In accordance with one embodiment of the invention, distinct scramblingbit sequences are used in different sectors and the sector/scramblinginformation is stored in the mobiles. The base station, 500 of FIG. 5,uses different scrambling bit sequences in the 3 sectors to generatetheir respective transmit signals. The wireless terminal receiver 610 ofFIG. 6 uses the particular scrambling bit sequence, corresponding to thesector in which it is located, to selectively demodulate the signal froman intended sector transmission of the base station 500. Alternatively,the wireless terminal receiver 610 may use multiple scrambling bitsequences to demodulate the signals from multiple sector transmissionsof a base station 500 or from multiple base stations simultaneously withthe scrambling sequence used corresponding to the one used by the sectorwhich transmitted the signal being recovered.

Channel condition measurement and reporting features of the inventionwill now be described. In order to facilitate the scheduling fordownlink traffic channel segments, such as power allocation and burstdata rate allocation, a wireless terminal 600 of FIG. 6 may measure itsdownlink channel condition under control of routine 628 of FIG. 6 andperiodically send the channel condition report including data/info632/634 of FIG. 6 to the base station 500 of FIG. 5.

The channel condition of a wireless terminal 600 may be in twocharacteristic regions. For the sake of description, assume that thechannel condition is measured in terms of SIR (Signal InterferenceRatio). In the first region, e.g., the non-sector boundary region, theSIR is limited by the inter-cell interference or the wirelesspropagation loss, while the inter-sector interference is a smallcomponent. In that case, the base station 500 can increase the receivedSIR of a traffic channel segment to the wireless terminal 600 byallocating high transmission power under control of routines 538 and 540of FIG. 5. In the second region, e.g., the inter-sector boundary region,the SIR is mainly limited by the inter-sector interference. In thatcase, given the constraint on power allocation, e.g., a small Deltabetween sectors across corresponding data traffic channel segments inthe cell's sectors, allocating high transmission power does notremarkably increase the received SIR since the power of the interferenceincreases as the power is increased. The above two regions represent theextreme channel condition characteristics. In reality, the channelcondition of the wireless terminal 600 may more typically be in-betweenthe two extreme regions which were just described.

In accordance with the invention, the wireless terminal 600 estimates,e.g., measures its channel condition characteristics under control ofroutine 628 and notifies the base station 500 of the determined channelinformation. This allows the base station 500 to make sensiblescheduling decisions in terms of power and burst data rate allocation.In one embodiment of the invention, data 632,634 shown FIG. 6 isincluded in a downlink channel condition report sent to the basestation. In some implementations, the wireless terminal 600differentiates the SIR due to inter-sector interference via routine 536of FIG. 5 and SIR due to other types of impairments such as inter-cellinterference via routine 536 of FIG. 5 and provides such information tothe base station. This allows the base station to perform powerallocation decisions based on inter-sector feedback information and notsimply a single interference indicator which makes it difficult todetermine if allocating more power will have a desired beneficialresult.

Use of a relatively high power tone or tones, referred to here as abeacon signal, will now be described. To facilitate various downlinkoperations, in accordance with the invention, the base station 500 ofFIG. 5 may frequently and/or periodically transmit a beacon signal undercontrol of signal generation routine 532 as a function of information530 which includes beacon info 548. Each beacon signal is an OFDM signaltransmitted over, e.g., during one single symbol transmission period.When a beacon signal is transmitted, most of the transmission power isconcentrated on a small number of tones, e.g., one or two tones whichcomprise the beacon signal. Many or most of the tones which are not usedfor the beacon signal may, and often are, left unused. The tones whichform the beacon may include 80% or more of a maximum average total basestation power used by said base station to transmit in a sector during abeacon signal transmission time, which may, e.g., in some embodiments bea symbol time. In some embodiments, some additional tones, may carrysignal at the same time as the beacon transmission, and the total powerlevel for those tones is less than or equal to 20% of the maximumaverage base station power used by the base station to transmit in thesector at the time of beacon transmission.

The graph 1400 of FIG. 14 shows an ordinary OFDM signal. The verticalaxis 1402 represents the power allocated to tones while the horizontalaxis 1404 corresponds to tone frequency. Individual bars 1406, 1408,1410, 1412, 1414, 1416, 1418, 1420, 1422, 1424 each correspond to thelevel of power for each of the distinct exemplary OFDM frequency tonesat some instant of time, e.g., the symbol period. It may be seen thatthe total power is broken up relatively uniformly between the variousfrequency tones.

The graph 1500 of FIG. 15 shows an exemplary beacon signal in accordancewith one exemplary embodiment of the present invention. The beaconsignal includes two tones 1506, 1508. The majority of the sectortransmission power is allocated between the two tones 1506, 1508 of thebeacon each of which is allocated approximately 45-50% of the totalpower. The vertical axis 1502 represents per tone power while thehorizontal axis 1504 corresponds to tone frequency. In the FIG. 15example, this results in two tones having approximately the same totalpower as the tones normally used to transmit data. Individual bars 1506,1508 correspond to the level of power for each of two selected OFDMfrequency tones at the instant of time of beacon transmission. It may beseen that the total power is concentrated on the two selectedfrequencies at the time of beacon transmission. The significantconcentration of sector transmission power in a very limited number oftones differs significantly from conventional pilot tones where thepilots may be transmitted at power levels slightly higher than tonesused to transmit data.

The graph 1600 of FIG. 16 shows an exemplary beacon signal in accordancewith another embodiment of the present invention where the total poweris allocated primarily to only one single frequency tone which isallocated approximately 90-100% of the total sector transmission power.The vertical axis 1602 represents per tone power while the horizontalaxis 1604 represents frequency tone. A single bar 1606 corresponds tothe level of power for the single selected OFDM frequency tone used asthe beacon signal. It may be seen that the total power is concentratedon the one single frequency tone at the time of beacon transmissionresulting in a beacon tone having a power level at least 5 times that ofthe highest power tone used to transmit data in the sector at othertimes.

One advantage of this concentration of power in a beacon signal, is theeasy and rapid identification of the beacon signal(s) by the mobilenodes, e.g. MN 600 of FIG. 6. This allows for the rapid and/or accurateconveyance of information to the mobiles at the point of time a beaconis transmitted, e.g., super slot boundary synchronization information,slope (cell) information, or sector information. Given the high power ofthe beacon tones, they are easy to detect with the probability of a datatone being misinterpreted as a beacon tone being relatively low due tothe normally large power difference between the beacon tones and datatones.

In one embodiment of the invention, the beacon signal may be transmittedat a fixed OFDM symbol duration, for example, the first or the last OFDMsymbol, of a super slot. In this way, a beacon tone can be used tosignal superslot boundaries. The beacon signal may repeat every superslot or every few super slots. The beacon signal is easy to detect, asit has extremely high power concentrated on just a few tones. Therefore,once the time position of the beacon signal has been located, the superslot boundaries can be promptly determined with a high degree ofcertainty.

In another embodiment of the invention, the high power tone or tonesused as a beacon signal is selected from a predefined group of beacontones or tone sets. Tone sets are used where multiple high power tonesform a beacon signal may vary with time. The sets of predefined beacontones may be included as part of the stored beacon information 548included in the base station of FIG. 5 and the stored beacon information652 of the wireless terminal. Using different beacon tone sets as thebeacon signal can be used to indicate or convey certain systeminformation including sector identification information. For example,the beacon signal may use 4 tones, as shown in FIG. 17. In the graph1700 of FIG. 17, the vertical axis 1702 represents per tone power, whilethe horizontal axis 1704 represents frequency. FIG. 17 shows a set offour beacon tones: B1 1706, A1 1708, A2 1710, and B2 1712. The per tonepower for each of the beacons 1706, 1708, 1710, 1712 is approximatelythe same with each beacon tone being allocated approximately 25% of thesectors total transmission power. The frequency location of variousbeacon tones, e.g., the two inner tones A1 1708 and A2 1710 is used toindicate the value of SLOPE used in the cell. The frequency location ofsome tones, e.g., the two outer tones B 11706 and B2 1712 is used toindicate the boundary of the frequency band used in the cell fortransmission purposes and/or optionally the sector index. Beacon signalsof neighboring cells will have different inner beacon tone frequencylocation A1 1708 and A2 1710 to indicate different slope values. Thus ina given cell, the beacon signals of different sectors may have differentB1 1706 and B2 1712 tone locations. Assuming that the outer beacon tonesB 11706 and B2 1706 are used to indicate frequency boundaries, these maybe the same in each sector of a cell assuming the use of the samefrequency band in each sector.

The time at which particular beacon signals are transmitted can be usedto indicate more than just slot boundaries. FIG. 18 shows a graph 1800of frequency vs OFDM symbol time illustrating different possible typesof beacons being transmitted in the time domain in accordance withvarious possible embodiments of the invention. The vertical axis 1802represents frequency and the horizontal axis 1804 corresponds to OFDMsymbol time. Different beacon signals will be described as correspondingto a particular beacon type based on the information it conveys alone orin combination with other beacon signals.

A type 1 beacon signal 1806 is shown to be transmitted at the start of asuper slot. After a time interval of k super slots 1812, where k is aninteger value, a type 2 beacon 1808 is transmitted. Then k super slots1814 later, a type 3 beacon 1810 is transmitted. The tone frequenciesand/or beacon tone power levels for each of the three beacons 1806,1808, 1810 are different. The type 1 beacon 1802 may be used to conveyfrequency floor information indicating a lower frequency boundary offrequency band being used in a sector. The type 2 beacon may be used toprovide an index to slope, e.g., slope indicator, from which a wirelessterminal can determine the cell's slope. Using the type 2 beacon todetermine slope allows a wireless terminal to determine which cell themobile node is located in. A type 3 beacon 1810 is used to convey sectorinformation (e.g. allow the mobile to identify the sector location1,2,3) via e.g. an index table of sector numbers or pilot offsetscorresponding to specific frequency tone values in the same manner atype 2 beacon can be used to convey cell information, e.g., slopeinformation. As discussed above, different base stations may bepre-configured with different values of slope, and different values forpilot offsets in different sectors, which are used to control thehopping sequences within a base station's cell.

FIG. 19 shows a graph 1900 of frequency vs OFDM symbol time illustratingthe concept of transmitting alternating beacons types in the time domainin accordance with one embodiment of the present invention to conveyinformation. The vertical axis 1902 represents frequency while thehorizontal axis 1904 represents OFDM symbol time. In the example shownin FIG. 19, the base station 500 of FIG. 5 transmits alternating beacontypes in the following sequence: type 1 beacon 1906, type 2 beacon 1908,type 1 beacon 1910, type 2 beacon 1912, type 1 beacon 1914, type 2beacon 1916, type 1 beacon 1918, type 2 beacon 1920. All of the type 1beacons 1906, 1910, 1914, 1918 are transmitted at the same frequencytone f₁ 1922. Type 2 beacons 1908 and 1916 are transmitted at frequencytone f_(2a) 1924 while type 2 beacons 1912 and 1920 are transmitted atfrequency tone f_(2b) 1926. In the time domain the type 2 beacons switchbetween the two frequency tones, f_(2a) 1924 and f_(2b) 1926,alternately. The mobile node 600 of FIG. 6 can identify the type onebeacons based on beacon tone frequency. The mobile node 600 may be ableto process the two distinct type two beacons via an index table whichconverts each of the tone frequencies to an index number and ultimatelyto one slope hopping value 646 of FIG. 6 specific to one specific cell656 of FIG. 6. The mobile node 600 will receive two index numbers, oneof which will correspond to the slope index 650. The access node 500will operate on a fixed number of slope index values with a definedslope indicator equation. Based the mobile's knowledge of that data, themobile 600 can determine which index 650 corresponds to the slope 646.

As an example, consider that the slope index range is 0≧X_(S)≧79 andthat the slope indicator equation is (X_(S)+39) Mod 80. X_(S) representsthe index to slope for the access node 500. The access node 500 when ittransmits the type 2 beacon, alternates between the tone frequenciescorresponding to X_(S) and (X_(S)+39) Mod 80. In an exemplary case witha value of slope index=50, the exemplary access node transmits type 2beacons for index values: 50 and 9. The mobile node 600 may receive theindex 50 beacon followed by the index 9 beacon or the index 9 beaconfollowed by the index 50 beacon, depending upon the time that the mobile600 first detected the type 2 beacon signal. In order for the mobile 600to determine which is the Xs or slope index (first beacon), the mobile600 uses the known information that the second beacon's index will be 39index counts from the X_(S). If the mobile 600 first receives 9 and then50, the change in index counts is 41; therefore, the second receivedindex value 50 is the real value to be used for slope index 650. If themobile 600 first receives 50 and then 9, the change in index counts is39, therefore, the first received index value 50 is the real value to beused for slope index 650.

By using an index to slope or slope indicator, diversity in frequency isprovided allowing reconfiguration in case of failures on a specific tonefrequency.

The beacon may also be useful in identifying the cell and sectorlocation (656 and 654 of FIG. 6), and potentially more precise locationwithin the sector, of the mobile 600 receiving the beacon signal(s) andthus be useful to provide warnings of hand-offs and improve theefficiency in handoff operations. Also, by taking over some of thefunctions sometimes performed by the use of pilot hopping sequences andtransmitted pilot signals, such as synchronization to super slotboundaries, the number of pilots and/or pilot power can be reduced. Thusthe time of pilot data punch through may be reduced and there may alsobe a saving in power required to transmit and process pilots.

Various base station signaling, at different strength levels on a pertone basis and different repetition rates, of the present invention willbe described and discussed, as used in an exemplary frequency divisionmultiplexed communications system, e.g., an OFDM system. Four signalsshall be described, first signals which may include ordinary OFDM signalas in FIG. 14, a second signal with high power levels, e.g., a beaconsignal as in FIG. 15, a third signal which include signal havingordinary OFDM signals power levels which may include, e.g, user data, orif occurring concurrently with a beacon may have power levels using thepower remaining after beacon allocation, and a fourth signal, e.g.,another beacon signal as in FIG. 16 with high power levels comparablewith the second signal. The base station transmitter 514 of FIG. 5 usesa set of N tones, e.g. included in tone info 550 of FIG. 5, where N islarger than 10, to communicate information using first signals over afirst period of time at least two seconds long and in some embodimentsthe first period of time is at least 30 minutes. The first signals mayinclude, e.g., user data on traffic channels and may be transmittedusing data tone hopping sequences 554 of FIG. 5. A second signal,sometimes referred to as a beacon signal, may be transmitted during asecond period of time, where the beacon signal includes a set of Xtones, included in tone info 550 where X is less than 5, and where atleast 80% of a maximum average total base station transmission powerused by the base station during any 1 second time period during thefirst period of time, is allocated to the set of X tones forming thebeacon signal. In some embodiments, the second period of time, used totransmit the second (beacon) signal, may be, e.g., the period of timeused to transmit an OFDM symbol 552 of FIG. 5. In some embodiments, thesecond period, e.g., beacon time period, repeats periodically during thefirst period. Some of the X tones (beacon) may be at predetermined fixedfrequencies; such fixed frequencies, (see FIG. 17), may be used toconvey information such as sector location. Some of the X tones (beacon)may have a fixed frequency offset ≧0 from the lowest frequency tone inthe set of tones N; in this way the second signal (beacon signal) can beused to convey frequency boundary information to the wireless terminal600. Some of the X tones (beacon) may be transmitted at a frequencywhich is determined as a function of at least one of a base stationidentifier and a sector identifier. This may allow a wireless terminalto rapidly identify the cell and sector that it is operating in, quicklyobtain the data and pilot hopping sequences, and quickly synchronizewith the base station. In some embodiments, the number of X in thesecond (beacon) signal is one (see FIG. 16) or two (see FIG. 16). Thusthe base station's second (beacon) signal, transmitted with relativelyhigh power and with energy concentrated in one or a few tones, is easilydetectable by wireless terminals. In some embodiments, at least half ofthe N-X tones in the set of N tones but not in the set of X tones gounused during the period of the beacon transmission. In otherembodiments, none of the N-X tones in the set of N tones but not in theset of X tones are used during the beacon transmission time. Byrestricting transmission of non-X (beacon) tones during the secondsignal (beacon tone interval), the level of the second (beacon) signalcan be increased, and confusion with other signaling may be reduced,providing better detection and identification of the beacon signal bywireless terminals.

Third signal may also be transmitted over a third interval of time. Thethird signal may include a set of Y tones included in tone frequencyinfo 550, where Y≦N, with each tone in third set of Y tones having 20%or less of said maximum average base station transmission power used bybase station transmitter during any 1 second period during the firstperiod of time. The third period of time may have the same duration asthe second period of time, e.g., occur concurrently with a beaconsignal. In some embodiments at least two of data, control and pilotsignals may be modulated on at least some of said set of Y tones. Insome embodiments, the repetition rate of the set of Y (third signal)tones is at least 10 times the repetition rate of the set of X (secondor beacon signal) tones, while in other embodiments, the repetition rateof the set of Y (third signal) tones is at least 400 times therepetition rate of the set of X (second or beacon signal) tones.

A fourth signal may also be transmitted by the base station 500 during afourth period of time. The fourth signal includes G tones included intone frequency info 550 of FIG. 5, where G is less than 5 and where atleast 80% of the maximum average total base station power used by thebase station during any 1 second period during the first period of timeis allocated to the G tones. At least one of the G tones is not in theset of X tones (second signal tone set) and the frequency of at leastone of the G tones is a function of at least one of a base stationidentifier and a sector identifier. The fourth signal may also repeatperiodically during the first time interval. The fourth signal may beviewed as a second beacon signal being transmitted at a different timethan the second signal and conveying different information.

Beacon signals, are structured, in accordance with the invention, toconcentrate a relatively high level of power in a small number of tones.During the time of beacon transmission the non-beacon tones may carry noinformation or in some instances, some of the non-beacon tones may carrysignal but at a level significantly below the beacon tone levels. Thebeacon tones by their characteristics are easy to detect and can quicklyconvey information, e.g., cell and/or sector information, frequencyboundary information, and/or synchronization information to wirelessterminals.

Uplink issues will now be described. In accordance with the invention,the frequency, symbol timing, and super slot structures of the uplinksignal generated by a wireless terminal may be slaved to those of thedownlink signal. Having full synchronization of the downlink signal ineach of the sectors, tone frequencies, OFDM symbol timing, and superslot boundaries synchronized to the uplink signal in each of a cell'ssectors will insure similar synchronization in the uplink where theuplink is slaved to the downlink.

In one preferred embodiment of the invention, the data tone hoppingsequences and channel segments are synchronized across the sectors of acell. In that case, inter-sector interference is concentrated betweencorresponding channel segments.

The present invention may be implemented in hardware and/or software.For example, some aspects of the invention may be implemented asprocessor executed program instructions. Alternatively, or in addition,some aspects of the present invention may be implemented as integratedcircuits, such as ASICs for example. Control means for controlling oneor more transmitters may, and in various embodiments are implemented assoftware modules of a control routine. The apparatus of the presentinvention are directed to software, hardware and/or a combination ofsoftware and hardware. Machine readable medium including instructionsused to control a machine to implement one or more method steps inaccordance with the invention are contemplated and to be consideredwithin the scope of some embodiments of the invention.

1. A method of operating a transmitter in a cell which uses a set oftones to transmit into a first sector of said cell over a plurality ofsymbol times using tones from said set of tones, the cell including asecond sector adjoining said first sector, said transmitter transmittinginto said second sector on first and second communications channels, thefirst communications channel including a first subset of said set oftones during each of a first subset of said plurality of symbol times,the second communications channel including a second subset of said setof tones during each of said first subset of said plurality of times,said first subset of said set of tones and said second subset of saidset of tones being different from each other during each symbol time,the method comprising: operating the transmitter to transmit on saidfirst and second channels into said first sector in a synchronous mannerwith transmissions made by said transmitter into said second sector; andcontrolling a total transmission power of the tones corresponding to thefirst channel in the first sector during said first subset of saidplurality of symbol times to be greater than 20% and less than 500% of atotal power of the tones corresponding to the first channel transmittedinto the second sector, during said first subset of said plurality ofsymbol times.
 2. The method of claim 1, wherein controlling the totaltransmission power of the tones corresponding to the first channelincludes limiting the total power used in said first subset of symboltimes to be no more than a fixed fraction of a maximum average totaltransmission power used by said transmitter in the first sector duringany 1 hour period, said fixed fraction also being used to limit thetotal transmission power of the tones corresponding to the first channelin the second sector during the first subset of symbol times to be nomore than said fixed fraction of a maximum average total transmissionpower used by said transmitter in the second sector during any 1 hourperiod, said fixed fraction being less than 100%.
 3. The method of claim1, wherein said symbol times are orthogonal frequency divisionmultiplexed symbol transmission time periods and wherein said tones areorthogonal frequency division tones.
 4. The method of claim 1, whereinsaid set of tones is different during at least two symbol times in saidfirst subset of said plurality of symbol tones.
 5. The method of claim1, wherein said transmitter transmits into said first sector symbolscorresponding to a first constellation on said first channel during saidfirst subset of said plurality of symbol times and transmits symbolscorresponding to a second constellation during a second subset of saidplurality of symbol times, the second constellation including moresymbols than the first constellation, the method further comprising:controlling a total transmission power of the tones corresponding to thefirst channel in the first sector during the second subset of saidplurality of symbol times to be greater than 50% and less than 200% of atotal power of the tones transmitted in the second sector correspondingto the first channel during said second subset of said plurality ofsymbol times.
 6. The method of claim 1, wherein said transmittertransmits into said first sector symbols at a first channel coding rateon said first channel during said first subset of said plurality ofsymbol times and transmits symbols at a second channel coding rateduring a second subset of said plurality of symbol times, said secondchannel coding rate being higher than said first channel coding rate,the method further comprising; controlling a total transmission power ofthe tones corresponding to the first channel in the first sector duringthe second subset of said plurality of symbol times to be greater than50% and lass than 200% of a total power of the tones transmitted in thesecond sector corresponding to the first channel during said secondsubset of said plurality of symbol times.
 7. The method of claim 1,wherein the total transmission power of the transmitted tonescorresponding to the first channel in the first sector during the firstsubset of said plurality of symbol times is equal to the totaltransmission power of the transmitted tones in the first channel in thesecond sector during said first subset of said plurality of symboltimes.
 8. The method of claim 1, wherein the first subset of saidplurality of symbol times includes at least 14 consecutive symbol times.9. The method of claim 1, further comprising: controlling the totalpower of the tones transmitted in the first sector corresponding to thefirst channel during a fourth subset of said plurality of symbol timesto be one of greater than 200% and less than 50% of the total power ofthe tones transmitted in said first sector corresponding to the secondchannel during said fourth subset of said plurality of symbol times. 10.The method of claim 9, wherein the fourth subset of said plurality ofsymbol times includes at least 14 consecutive symbol times.
 11. Themethod of claim 1, wherein said first and second sectors use a thirdcommunications channel during a second subset of said plurality ofsymbol times, the third communications channel including a third subsetof said set of tones during each of said second subset of said pluralityof symbol times, the method further comprising; controlling saidtransmitter during said second subset of said plurality of symbol times,to limit the total transmission power on tones corresponding to saidthird communications channel transmitted by said transmitter to be lessthan 10% of the total transmission power used by said transmitter totransmit tones into said second sector corresponding to the thirdchannel during said second subset of said plurality of symbol times. 12.The method of claim 11, wherein the method is further directed tocontrolling the allocation of resources corresponding to said thirdcommunications channel to wireless terminals, the method furthercomprising: identifying wireless terminals in a boundary area whichcorresponds to a boundary between said first and second sectors; andallocating said resources corresponding to the said third channel to atleast one of said identified wireless terminals.
 13. The method of claim12, further comprising: receiving from a wireless terminal firstinformation indicating an amount of intersector interference measured bysaid wireless terminal and second information indicating an amount ofbackground interference measured by said wireless terminal.
 14. Themethod of claim 12, wherein identifying wireless terminals in theboundary area includes: receiving a signal from a wireless terminal insaid boundary area a signal indicating that said wireless terminal is insaid boundary area.
 15. The method of claim 14, wherein said signalindicating that a wireless terminal is in said boundary area is alocation information signal.
 16. The method of claim 11, wherein saidfirst and second sector use said third communications channel during athird subset of said plurality of symbol times, said third subset ofsaid plurality of symbol times being different from said second subsetof said plurality of symbol times, the method further comprising:controlling said transmitter during said third subset of said pluralityof symbol times, to use a total transmission power on tonescorresponding to said third communications channel transmitted by saidtransmitter into the first sector to be at least 1000% used by saidsecond sector to transmit tones corresponding to the third channel intothe second sector during said third subset of said plurality of symboltimes.
 17. The method of claim 16, wherein the second and third subsetsof said plurality of symbol times are interspersed according to a fixedpattern.
 18. The method of claim 1, wherein said first and secondsectors use a third communications channel during a second subset ofsaid plurality of symbol times, the third communications channelincluding a third subset of said set of tones during each of said secondsubset of said plurality of symbol times, the method further comprising:controlling said transmitter during said second subset of said pluralityof symbol times, to limit total transmission power on tonescorresponding to said third communications channel transmitted by saidtransmitter to be zero.
 19. A method of operating a transmitter in acell which uses a set of tones to transmit into a first sector of saidcell over a plurality of symbol times using tones from said set oftones, the cell including a second sector adjoining said first sector,said transmitter transmitting into said second sector on first andsecond communications channels, the first communications channelincluding a first subset of said set of tones during each of a firstsubset of said plurality of symbol times, the second communicationschannel including a second subset of said set of tones during each ofsaid first subset of said plurality of times, said first subset of saidset of tones and said second subset of said set of tones being differentfrom each other during each symbol time, the method comprising:operating the transmitter to transmit on said first and second channelsinto said first sector in a synchronous manner with transmissions madeby said transmitter into said second sector; controlling a totaltransmission power of the tones corresponding to the first channel inthe first sector during said first subset of said plurality of symboltimes to be greater than 20% and less than 500% of a total power of thetones corresponding to the first channel transmitted into the secondsector, during said first subset of said plurality of symbol times;controlling the total power of the tones transmitted in the first sectorcorresponding to the first channel during a fourth subset of saidplurality of symbol times to be one of greater than 200% and less than50% of the total power of the tones transmitted in said first sectorcorresponding to the second channel during said fourth subset of saidplurality of symbol times wherein the fourth subset of said pluralitysymbol times includes at least 14 consecutive symbol times; and whereinthe first and fourth subsets of said plurality of symbol times are thesame.
 20. A base station for use in a communications cell includingfirst and second sectors, the second sector adjoining the first sector,the base station comprising: a transmitter which uses a set of tones totransmit into a first sector of said cell over a plurality of symboltimes using tones from a set of tones, said transmitter transmittinginto said second sector on first and second communications channels, thefirst communications channel including a first subset of said set oftones during each of a first subset of said plurality of symbol times,the second communications channel including a second subset of said setof tones during each of said first subset of said plurality of times,said first subset of said set of tones and said second subset of saidset of tones being different from each other during each symbol time;means for controlling the transmitter to transmit on said first andsecond channels into said first sector in a synchronous manner withtransmissions made by said transmitter into said second sector; andpower control means for controlling a total transmission power of thetones corresponding to the first channel in the first sector during saidfirst subset of said plurality of symbol times to be greater than 20%and less than 500% of a total power of the tones corresponding to thefirst channel transmitted into the second sector, during said firstsubset of said plurality of symbol times.
 21. The base station of claim20, wherein said means for controlling the total transmission power ofthe tones corresponding to the first channel includes means for limitingthe total power used in said first subset of symbol times to be no morethan a fixed fraction of a maximum average total transmission power usedby said transmitter in the first sector during any 1 hour period, saidfixed fraction also being used to limit the total transmission power ofthe tones corresponding to the first channel in the second sector duringthe first subset of symbol times to be no more than said fixed fractionof a maximum average total transmission power used by said transmitterin the second sector during any 1 hour period, said fixed fraction beingless than 100%.
 22. The base station of claim 20, wherein said symboltimes are orthogonal frequency division multiplexed symbol transmissiontime periods and wherein said tones are orthogonal frequency divisiontones.
 23. The base station of claim 20, wherein said set of tones isdifferent during at least two symbol times in said first subset of saidplurality of symbol tones.
 24. The base station of claim 20, whereinsaid transmitter transmits into said first sector symbols correspondingto a first constellation on said first channel during said first subsetof said plurality of symbol times and transmits symbols corresponding toa second constellation during a second subset of said plurality ofsymbol times, the second constellation including more symbols than thefirst constellation, the method further comprising: means forcontrolling a total transmission power of the tones corresponding to thefirst channel in the first sector during the second subset of saidplurality of symbol times to be greater than 50% and less than 200% of atotal power of the tones transmitted in the second sector correspondingto the first channel during said second subset of said plurality ofsymbol times.
 25. The base station of claim 20, wherein said transmittertransmits into said first sector symbols at a first channel coding rateon said first channel during said first subset of said plurality ofsymbol times and transmits symbols at a second channel coding rateduring a second subset of said plurality of symbol times, said secondchannel coding rate being higher than said first channel coding rate,the method further comprising: means for controlling a totaltransmission power of the tones corresponding to the first channel inthe first sector during the second subset of said plurality of symboltimes to be greater than 50% and less than 200% of a total power of thetones transmitted in the second sector corresponding to the firstchannel during said second subset of said plurality of symbol times. 26.The base station of claim 20, further comprising: means for controllingthe total power of the tones transmitted in the first sectorcorresponding to the first channel during a fourth subset of saidplurality of symbol times to be one of greater than 200% and less than50% of the total power of the tones transmitted in said first sectorcorresponding to the second channel during said fourth subset of saidplurality of symbol times.
 27. The base station of claim 20, whereinsaid first and second sectors use a third communications channel duringa second subset of said plurality of symbol times, the thirdcommunications channel including a third subset of said set of tonesduring each of said second subset of said plurality of symbol times, thebase station further comprising: means for controlling said transmitterduring said second subset of said plurality of symbol times, to limitthe total transmission power on tones corresponding to said thirdcommunications channel transmitted by said transmitter to be less than10% of the total transmission power used by said transmitter to transmittones into said second sector corresponding to the third channel duringsaid second subset of said plurality of symbol times.
 28. The basestation of claim 27, further comprising: means for identifying wirelessterminals in a boundary area which corresponds to a boundary betweensaid first and second sectors; and means for allocating said resourcescorresponding to the said third channel to at least one of saididentified wireless terminals.
 29. The base station of claim 28, furthercomprising: a receiver for receiving from a wireless terminal firstinformation indicating an amount of intersector interference measured bysaid wireless terminal and second information indicating an amount ofbackground interference measured by said wireless terminal.
 30. The basestation of claim 28, further comprising: a receiver for receiving asignal from a wireless terminal in said boundary area a signalindicating that said wireless terminal is in said boundary area.
 31. Thebase station of claim 20, wherein said first and second sectors use athird communications channel during a second subset of said plurality ofsymbol times, the third communications channel including a third subsetof said set of tones during each of said second subset of said pluralityof symbol times, the base station further comprising: means forcontrolling said transmitter during said second subset of said pluralityof symbol times, to limit total transmission power on tonescorresponding to said third communications channel transmitted by saidtransmitter to be zero.
 32. A method of operating a base station in acell, the method comprising: transmitting on first and second channelsinto first and second sectors of said cell in a synchronous manner, saidfirst sector being adjacent said second sector, the first channelincluding different tones from said second channel during each of afirst plurality of symbol times, the tones of the first communicationschannel being the same in said first and second sectors; and controllinga first transmission power and a second transmission power to keep thefirst and second transmission powers within a first intersector powerrange during said first plurality of symbol transmission time periods,said first transmission power being the total transmission power of thetones of the first channel in the first sector during said firstplurality of symbol times, said second transmission power being thetotal transmission power of the tones of the first channel in the secondsector during said first plurality of symbol times, said firstintersector power range being between 20% and 500%.
 33. The method ofclaim 32, further comprising: controlling a third transmission power tokeep the third transmission power higher than said first transmissionpower during said first plurality of symbol times, the thirdtransmission power being the transmission power of said tones of thesecond channel in the first sector during said first plurality of symboltimes.
 34. The method of claim 32, wherein the tones of the secondcommunications channel are the same in the first and second sectors, themethod further comprising: changing the intersector power range used tocontrol the first and second transmission powers as a function of thesize of a constellation of symbols used to transmit symbols on saidfirst channel.
 35. The method of claim 34, wherein changing theintersector power range used to control the first and secondtransmission powers as a function of the size of a constellation ofsymbols used to transmit symbols on said first channel, includesreducing the intersector power range used during a second plurality ofsymbol time periods from the first intersector power range, when alarger symbol constellation is used during said second plurality ofsymbol time periods than is used during said first plurality of symboltime periods.
 36. The method of claim 35, wherein changing theintersector power range used to control the first and secondtransmission powers as a function of the coding rate includes reducingthe intersector power range used during a second plurality of symboltime periods from the first intersector power range, when a largersymbol constellation is used during said second plurality of symbol timeperiods than is used during said first plurality of symbol time periods;and wherein said first and second sectors are synchronized to within acyclic prefix duration, transmissions corresponding to the first channelbeing made on the same tones and during the same symbol times duringsaid second plurality of symbol time periods in each of said first andsecond sectors.
 37. The method of claim 32, further comprising: changingthe intersector power range used to control the first and secondtransmission powers as a function of a coding rate used to codeinformation transmitted on said first communications channel in saidfirst sector.
 38. A device including a processor configured to control abase station in a cell to implement a communications method, the methodcomprising: transmitting on first and second channels into first andsecond sectors of said cell in a synchronous manner, said first sectorbeing adjacent said second sector, the first channel including differenttones from said second channel during each of a first plurality ofsymbol times, the tones of the first communications channel being thesame in said first and second sectors, the tones of the secondcommunications channel being the same in the first and second sectors;and controlling a first transmission power and a second transmissionpower to keep the first and second transmission powers within a firstintersector power range during said first plurality of symboltransmission time periods, said first transmission power being the totaltransmission power of the tones of the first channel in the first sectorduring said first plurality of symbol times, said second transmissionpower being the total transmission power of the tones of the firstchannel in the second sector during said first plurality of symboltimes, said first intersector power range being between 20% and 500%.39. The device of claim 38, wherein the method further comprises:controlling a third transmission power to keep the third transmissionpower higher than said first transmission power during said firstplurality of symbol times, the third transmission power being thetransmission power of said tones of the second channel in the firstsector during said first plurality of symbol times.
 40. The device ofclaim 39, wherein the method further comprises: changing the intersectorpower range used to control the first and second transmission powers asa function of the size of a constellation of symbols used to transmitsymbols on said first channel.
 41. A computer readable medium embodyingmachine executable instructions for controlling a base station in a cellto implement a communications method, the method comprising:transmitting on first and second channels into first and second sectorsof said cell in a synchronous manner, said first sector being adjacentsaid second sector, the first channel including different tones fromsaid second channel during each of a first plurality of symbol times,the tones of the first communications channel being the same in saidfirst and second sectors, the tones of the second communications channelbeing the same in the first and second sectors, and controlling a firsttransmission power and a second transmission power to keep the first andsecond transmission powers within a first intersector power range duringsaid first plurality of symbol transmission time periods, said firsttransmission power being the total transmission power of the tones ofthe first channel in the first sector during said first plurality ofsymbol times, said second transmission power being the totaltransmission power of the tones of the first channel in the secondsector during said first plurality of symbol times, said firstintersector power range being between 20% and 500%.
 42. The computerreadable medium of claim 41, wherein the method further comprises:controlling a third transmission power to keep the third transmissionpower higher than said first transmission power during said firstplurality of symbol times, the third transmission power being thetransmission power of said tones of the second channel in the firstsector during said first plurality of symbol times.
 43. The computerreadable medium of claim 42, wherein the method further comprises:changing the intersector power range used to control the first andsecond transmission powers as a function of the size of a constellationof symbols used to transmit symbols on said first channel.
 44. A basestation in a cell, comprising: a transmitter module for transmitting onfirst and second channels into first and second sectors of said cell ina synchronous manner, said first sector being adjacent said secondsector, the first channel including different tones from said secondchannel during each of a first plurality of symbol times, the tones ofthe first communications channel being the same in said first and secondsectors, the tones of the second communications channel being the samein the first and second sectors, and a control module for controlling afirst transmission power and a second transmission power to keep thefirst and second transmission powers within a first intersector powerrange during said first plurality of symbol transmission time periods,said first transmission power being the total transmission power of thetones of the first channel in the first sector during said firstplurality of symbol times, said second transmission power being thetotal transmission power of the tones of the first channel in the secondsector during said first plurality of symbol times, said firstintersector power range being between 20% and 500%.
 45. The base stationof claim 44, wherein said control module further controls a thirdtransmission power to keep the third transmission power higher than saidfirst transmission power during said first plurality of symbol times,the third transmission power being the transmission power of said tonesof the second channel in the first sector during said first plurality ofsymbol times.
 46. The base station of claim 45, wherein said controlmodule changes the intersector power range used to control the first andsecond transmission powers as a function of the size of a constellationof symbols used to transmit symbols on said first channel.
 47. A basestation in a cell, comprising: transmitter means for transmitting onfirst and second channels into first and second sectors of said cell ina synchronous manner, said first sector being adjacent said secondsector, the first channels including different tones from said secondcannel during each of a first plurality of symbol times, the tones ofthe first communications channel being the same in said first and secondsectors, the tones of the second communications channel being the samein the first and second sectors, and control means for controlling afirst transmission power and a second transmission power to keep thefirst and second transmission powers within a first intersector powerrange during said first plurality of symbol transmission time periods,said first transmission power being the total transmission power of thetones of the first channel in the first sector during said firstplurality of symbol times, said second transmission power being thetotal transmission power of the tones of the first channel in the secondsector during said first plurality of symbol times, said firstintersector power range being between 20% and 500%.
 48. The base stationof claim 47, further comprising: means for controlling a thirdtransmission power to keep the third transmission power higher than saidfirst transmission power during said first plurality of symbol times,the third transmission power being the transmission power of said tonesof the second channel in the first sector during said first plurality ofsymbol times.